[ky'] ky` thi toa'n

["Nguyen Tien Zung" <tienzung@darboux.math.univ-montp2.fr>]

/*
(c) Copyright Ti't Ba^`u 1997, all rights reserved
Enjoy!
*/

DDoa`n ho.c sinh Vie^.t nam ddi thi toa'n olympic quo^'c te^' na(m 
ddo' co' ta'm ngu+o+`i: co^ Hoa`ng Xua^n Si'nh,  tha^`y DDoa`n Quy`nh 
va` sa'u ho.c sinh. Trong sa'u ho.c sinh  chi? co' anh Quye^`n ddang 
ho.c lo+'p 12, co`n na(m te^n co`n la.i la` Giang, Kha'nh, Tha`nh, 
Vu~ va` to^i dde^`u ddang ho.c lo+'p 11. Vu~ va` to^i o+? Ha` no^.i, 
bo^'n ba.n co`n la.i o+? mie^`n Nam.  Thi o+? Pha^`n lan, tie^`n chi 
phi' a(n o+?, ddi la.i cu~ng do phi'a Pha^`n lan ta`i tro+.. Co`n 
phi'a Vie^.t nam vo+'i "tinh tha^`n tie^'t kie^.m" cao cha('c se~ 
kho^ng bo? tie^`n tu'i ra dde^? du+. mo^.t cuo^.c thi to^'n ke'm nhu+ 
va^.y\. Ho^`i na(m 1977, Vie^.t nam cu~ng la^.p mo^.t ddo^.i tuye^?n 
dde^? ddi.nh thi toa'n quo^'c te^', nhu+ng na(m ddo' vi` nu+o+'c to^? 
chu+'c la` Nam tu+ kho^ng hu+'a cha('c cha('n se~ cho tie^`n chi 
phi', ne^n ddoa`n la.i gia?i ta'n.

Sau khi la^.p ddo^.i tuye^?n, chu'ng to^i ddu+o+.c ta^.p trung o+?  
tru+o+`ng DDa.i ho.c Su+ pha.m Ha` no^.i 1 dde^? "luye^.n ga` cho.i" 
trong vo`ng hai tha'ng. Sa'u ddu+'a ddu+o+.c cho va`o mo^.t pho`ng,  
ngu? giu+o+`ng ta^`ng gio^'ng nhu+ sinh vie^n. To^i va` Vu~ la` hai 
te^n ngu+o+`i Ha` no^.i cu~ng ngu? luo^n trong ddo', chi? cuo^'i 
tua^`n mo+'i ve^` nha`. A(n uo^'ng kho^ng ma^'t tie^`n o+? ngay trong 
tru+o+`ng. Tie^u chua^?n a(n ra^'t sang so vo+'i tho+`i ddo': nga`y 
ba bu+~a tu+o+i (ddu? cha^'t dda.m), to^'i la.i ddu+o+.c a(n gia?i 
kha't mo^.t co^'c che` ddo^~ dden dda'. Ma^'y anh ba.n mie^`n Nam 
co`n ddu+o+.c ca'c Ty gia'o du.c trong ddo' gu+?i tie^`n cho bo^`i 
du+o+~ng kha' nhie^`u, trong tu'i su'ng si'nh. Co`n to^i da^n chuye^n 
toa'n To^?ng ho+.p cha? co' gi`, Vu~ ho.c chuye^n toa'n Chu Va(n An 
cu~ng ga^`n nhu+ va^.y\. DDo^'i vo+'i nhu+~ng ti?nh mie^`n Nam, co' 
ho.c sinh ddi thi toa'n quo^'c te^' la` su+. kie^.n to la('m, va` 
ma^'y anh ddi thi ra^'t ddu+o+.c cu+ng. Ma^'y na(m tru+o+'c, co' anh   
o+?  Sa`i go`n khi thi toa'n quo^'c te^' ddu+o+.c pha^n ngay mo^.t 
ca(n nha`, co`n co' anh o+? DDa` na(~ng khi ddi thi ve^` nha^n da^n  
ha^m mo^. pha?i xe^'p ha`ng tha`nh hai ha`ng dde^? ddo'n anh tu+` 
sa^n bay\.

O+? tru+o+`ng Su+ pha.m, ha`ng nga`y chu'ng to^i pha?i ho.c hai 
buo^?i,  mo^~i buo^?i mo^.t tha^`y gia'o da.y\. Co' to^?ng co^.ng 
qua~ng ho+n mu+o+`i tha^`y da.y, trong ddo' mo^.t so^' tha^`y tre?  
tru+o+'c cu~ng tu+`ng thi toa'n quo^'c te^'. Ngoa`i toa'n so+ ca^'p, 
trong chu+o+ng tri`nh da.y co`n co' mo^.t i't "toa'n cao ca^'p": ly'  
thuye^'t ddo^` thi., toa'n sa'c xua^'t, va` mo^.t i't toa'n gia?i 
ti'ch.  Go.i la` cao ca^'p co' le~ kho^ng ha(?n ddu'ng, nhu+ng co' 
ddie^`u no' kho^ng na(`m trong chu+o+ng tri`nh pho^? tho^ng o+? 
Vie^.t nam. To^i kho^ng nho+' he^'t ca'c tha^`y dda~ da.y ho^`i ddo', 
chi? nho+' mo^.t so^' tha^`y dde^? la.i a^'n tu+o+.ng sa^u sa('c 
nha^t. Tru+o+'c he^'t la` tha^`y Tha'i (anh DDo^~ DDu+'c Tha'i), phu. 
tra'ch chung va` da.y nhie^`u nha^'t. Anh Tha'i do.a bo.n to^i "DDa^y 
chi? la` ddo^.i du+. tuye^?n, chu+a pha?i la` ddo^.i tuye^?n chi'nh 
thu+'c, ca^.u na`o lo+ mo+ se~ bi. loa.i". Do.a the^' tho^i, chu+' 
kho^ng co' chuye^.n gi` xa?y ra\. Tha^`y Ho`a (anh Vu~ DDi`nh Ho`a) 
la` ngu+o+`i da.y ly' thuye^'t ddo^` thi.. Anh Ho`a thu+o+`ng ddi 
mo^.t ca'i xe dda.p "co+?i chuo^`ng" dde^'n tru+o+`ng. Mo^.t la^`n 
anh go.i to^i le^n ba?ng. Khi to^i vie^'t ddu+o+.c mo^.t lu'c thi` 
anh "mu+`ng ro+~" no'i "Mi`nh cu+' tu+o+?ng la` mi`nh vie^'t chu+~ 
xa^'u nha^'t, ho^m nay mo+'i tha^'y ngu+o+`i vie^'t chu+~ xa^'u ho+n 
mi`nh". Ly' thuye^'t sa'c xua^'t co' hai ngu+o+`i da.y la` tha^`y 
DDu+'c (anh Nguye^~n Minh DDu+'c) va` mo^.t tha^`y X na`o ddo' la` 
ca'n bo^. co' co+~ cu?a Bo^.  Gia'o du.c. Khi da.y, tha^`y X tri.nh 
tro.ng vie^'t he^'t ddi.nh nghi~a na`y dde^'n ddi.nh nghi~a kha'c, 
ma` cuo^'i cu`ng chu'ng to^i kho^ng hie^?u dde^? la`m gi`. Co`n anh 
DDu+'c, gio.ng no'i ra^'t nho? nhe., da.y cu. the^? ho+n. Chi? vo+'i 
ba`i toa'n sau dda^y anh dda~ minh ho.a ddu+o+.c su+. quan tro.ng 
cu?a vie^.c xa'c di.nh ddu'ng ddo^. ddo: "Hai hi?nh tro`n ddo^`ng 
ta^m, mo^t ca'i ba'n ki'nh mo^.t, mo^.t ca'i ba'n ki'nh hai\. Tung 1 
ddie^?m tu`y y' va`o hi`nh tro`n ba'n ki'nh hai, ho?i sa'c xua^'t 
dde^? no' ro+i va`o hi`nh tro`n ba'n ki'nh mo^.t la` bao nhie^u". 
Ngoa`i hai buo^?i le^n lo+'p, bo.n to^i ddu+o+.c tu+. do ai thi'ch 
gi` la`m na^'y\. Anh Quye^`n co' mo^.t quye^?n ly' thuye^'t ha`m 
bie^'n phu+'c la`m ca^?m nang thi?nh thoa?ng gio+? ra ddo.c, na(m 
tha(`ng co`n la.i tro^' ma('t nhi`n va`o cha? hie^?u gi`.  Giang lu'c 
ddo' chu+a bie^'t kha'i nie^.m ti'ch pha^n, ca^`m quye^?n sa'ch cu?a 
anh Quye^`n gio+ le^n xem ro^`i no'i "Nhi`n nhu+~ng con giun tro^ng 
so+. ghe^".

Lu'c kho^ng ho.c ha`nh, ma^'y te^n trong ddo^.i tuye^?n ddi da.o 
cho+i  loanh quanh, hoa(.c ru? nhau ddi tha(m ba.n be` ho.  ha`ng o+? 
Ha` no^.i\. Mo^.t trong nhu+~ng tie^'t mu.c u+a thi'ch la` ddu+'ng 
tre^n ban co^ng nhi`n ngu+o+`i qua la.i\. Sau va`i ho^m nga('m nhi`n 
nhu+ va^.y, ca? bo.n pha't hie^n ra mo^.t co^ ga'i, lu'c ddo' ddang 
la` ho.c sinh chuye^n toa'n Su+ pha.m, ho^m na`o cu~ng ma(.c cu`ng 
mo^.t ca'i qua^`n da`i\. Chu'ng to^i be`n nghi.ch ngo+.m ddu+a ra 
ddu? ca'c gia? thuye^'t ve^` ca'i qua^`n da`i cu?a co^ ta la`m tro` 
ddu`a\.  Gia' ba^y gio+` bie^'t ddu+o+.c co^ ta dda~ ra sao, la`m gi` 
o+? dda^u, co' khi thu' vi. bie^'t ma^'y\.

Ngoa`i chu+o+ng tri`nh ho.c nga`y hai buo^?i, Bo^. Gia'o Du.c co' 
to^?  chu+'c va`i la^`n ddi tha(m quan cho sa'u ho.c sinh. Mo^.t 
la^`n tha(m quan khu La(ng Ba'c va` khu nha` sa`n ca.nh ddo'.  
Ngu+o+`i phu. tra'ch nha` sa`n gio+'i thie^.u cho chu'ng to^i ca'c 
ddu+'c ti'nh qui' ba'u cu?a Ho^` Chu? Ti.ch:  Du+o+'i ca^`u thang co'  
co^ng ta('c dde`n, dde^? lu'c Ngu+o+`i xuo^'ng he^'t ca^`u thang thi` 
ta('t dde`n ddi cho kho?i phi' ddie^.n. Tre^n ba`n la`m vie^.c co'  
mo^.t ho`n dda' to, dde^? Ngu+o+`i thi?nh thoa?ng bo'p no' dde^? 
luye^.n tay\. Mo^.t trong nhu+~ng ca?nh thu' vi.  trong khu nha` sa`n 
la` ca'i ao ca'. Ca' ra^'t nhie^`u, con na`o con dda^'y to tu+o+'ng 
be'o ma^~m. Ngu+o+`i ta nuo^i ca' ba(`ng mo^.t loa.i thu+'c a(n  
dda(.c bie^.t, vo tha`nh cu.c. Ma^'y vie^n thu+'c a(n ddo' cha('c 
la`m to^'n ke'm la('m, vi` o+? ngoa`i kho^ng dda^u tha^'y co'. Sau 
buo^?i tha(m quan, ngu+o+`i phu. tra'ch mang quye^?n so^? lu+u nie^.m 
ra mo+`i vie^'t. Chu'ng to^i hoa?ng qua', kho^ng bie^'t vie^'t gi`, 
ngu+o+`i ta cu~ng kho^ng e'p. Mo^.t buo^?i kha'c, chu'ng to^i 
ddu+o+.c ddu+a ddi tha(m quan khu Thu?y ddie^.n so^ng DDa`, mo^.t 
co^ng tri`nh the^' ky? cu?a Vie^.t nam, bie^?u tu+o+.ng cu?a ti`nh 
hu+~u nghi. Vie^.t-Xo^. Tre^n ddo' co' cho^n bu+'c thu+ gu+?i the^' 
he^. na(m 2100. Qua? la` ma^'y ngu+o+`i la~nh dda.o co' ta^`m nhi`n 
xa tro^ng ro^.ng co' mo^.t kho^ng hai, dda~ vie^'t thu+ cho^n xuo^'ng 
dda^'t gu+?i ngu+o+`i tra(m na(m sau\. DDie^?m dda(.c bie^.t nu+~a 
cu?a Thu?y ddie^.n so^ng DDa` ma` kho^ng no+i na`o kha'c co' la` ma'y 
cha.y ddie^.n ddu+o+.c cho^n va`o trong nu'i, ra^'t to^'n ke'm.  
Cha('c ho^`i ddo' so+. Trung Quo^'c gio+? chu+'ng ne'm bom pha' hoa.i\.

Tru+o+'c khi ddi thi, chu'ng to^i ddu+o+.c da^~n dde^'n mo^.t nha`  
kho cu?a Bo^. Ta`i Chi'nh dde^? trang bi. cho chuye^'n ddi\. O+? ddo' 
mo^~i ngu+o+`i ddu+o+.c mu+o+.n mo^.t bo^. com le^ va` mo^.t ddo^i  
gia`y\. Kho^? ca'i tha^n to^i ho+i qua kho^? so vo+'i ngu+o+`i Vie^.t 
nam, ne^n ti`m ma~i mo+'i ra ddu+o+.c mo^.t ca'i a'o ve't cu~ ma(.c 
vu+`a ma`u xanh la' ca^y, co`n ca'i cha^n co+~ 42 cu?a to^i thi` 
kho^ng gia^`y na`o ddi vu+`a, ne^n dda`nh chi.u\. Me. to^i be`n bo? 
tie^`n thue^ tho+. ddo'ng gia^`y\. Sau ma^'y ho^m, to^i co' ddu+o+.c 
mo^.t ddo^i gia^`y dde^' cau su, co`n phi'a tre^n ba(`ng gia^'y\.  
La^`n dda^`u tie^n to^i ddi gia^`y, pha?i ddo^i cu+'ng que`o, ddau 
he^'t ca? cha^n. Khi sang dde^'n Pha^`n lan thi` go't cha^n dda~ bi. 
su+ng va` ra'ch ra mo^.t ma?ng, co`n gia^`y do bi. co. su+o+'c dda~ 
co' cho^~ ma^'t lo+'p so+n dden be^n ngoa`i, lo^. ra gia^'y tra('ng.

Ho^m sa't nga`y bay, co^ Si'nh ta^.p ho.p ho.c sinh la.i da(.n do`.  
Trong ca'c khoa?n da(.n, co' mo^.t khoa?n quan tro.ng la` kho^ng em 
ho.c sinh na`o ddu+o+.c mang ba^'t cu+' ca'i gi` ddi dde^? ba'n la.i 
ta.i Lie^n xo^. Ho^`i ddo' da^n Vie^.t nam ddi Nga dda~ thu+o+`ng 
mang theo mo^~i ngu+o+`i mo^.t i't thu+' nhu+ qua^`n bo`, a'o pho^ng, 
ddo^`ng ho^` ddie^.n tu+?, ddo^`ng ho^` Citizen, ..., dde^?  ba'n 
la.i be^n ddo' kie^'m lo+`i\. Mo^~i ngu+o+`i ne^'u mang mo^~i thu+' 
mo^.t hai ca'i thi` kho^ng bi. ha?i quan Nga ha.nh ho.e gi`, nhu+ng 
co^ Si'nh ra^'t so+. phie^`n phu+'c ne^n ca^'m tie^.t cho cha('c. 
Ho'a ra cha? ai nghe lo+`i co^, va^~n le'n lu't mang mo^.t i't ddo^`. 
Me. to^i cu~ng ddu't va`o va ly cho to^i mo^.t ca'i ddo^`ng ho^` 
ddie^.n tu+? va` mo^.t hai ca'i a'o pho^ng gi` ddo', nhu+ng chu+a 
ddu+o+.c mo^.t nu+?a "tie^u chua^?n" bi`nh thu+o+`ng. Co' mo^.t ba.n  
trong ddoa`n, co' ngu+o+`i nha` o+? Lie^n xo^ dda~ he.n tru+o+'c, 
co`n mang "qua' tie^u chua^?n". May kho^ng bi. ha?i quan kha'm xe't 
gi`.

DDe^'n nga`y, chu'ng to^i ra cu+?a kha^?u no^.i ba`i, le^n mo^.t  
chie^'c ma'y bay cu?a Nga dde^? bay sang Lie^n xo^. DDa^y la` la^`n 
dda^`u tie^n to^i ddu+o+.c ddi ma'y bay, ddu+o+.c gia'p ma(.t  
ngu+o+`i Nga no'i tie^'ng xi` xo^`. Ca'i gi` cu~ng mo+'i la.. Khi 
va`o nha` ve^.  sinh tre^n ma'y bay thi` loay hoay ma~i kho^ng bie^'t 
la`m sao gia^.t ddu+o+.c nu+o+'c. Chu+a ma(.c ddu+o+.c qua^`n va`o 
thi` dda~ tha^'y mo^.t co^ chie^u dda~i vie^n mo+? cu+?a xo^ng va`o 
dduo^?i ve^` cho^~ ngo^`i vo+'i ly' do ma'y bay ddang bay qua cho^~ 
sao ddo'.  DDa^'y la` to^i ddoa'n the^' tho^i, chu+' tie^'ng Nga co' 
hie^?u gi` dda^u\.  Ho^`i ho.c pho^? tho^ng, mo^n ngoa.i ngu+~ duy 
nha^'t la` tie^'ng Nga trong suo^'t da(m ba^?y na(m, nhu+ng chu+~ 
va`o tai no. la.i ra tai kia, cha? nho+' ddu+o+.c gi` ma^'y\. Khi o+? 
tre^n ma'y bay thi` chi? hie^?u hai chu+~ "Trai" (nu+o+'c tra`) va` 
"Co^ phe^" (ca` phe^). Ngu+o+`i Nga tre^n ma'y bay, tro^ng ai cu~ng 
to lo+'n sang tro.ng, a'p dda?o da^n Vie^.t. Ngay ca'c co^ phu.c vu. 
tro^ng cu~ng oai phong la^~m lie^.t, da^n ta ddu+o+.c phu.c vu.  cu+' 
nhu+ ddu+o+.c ban o+n.

Ma'y bay ha. ca'nh o+? sa^n bay Seremetievo va`o buo^?i sa'ng. Kho?i  
pha?i ta? no^~i mu+`ng ro+~ cu?a to^i khi ddu+o+.c dda(.t cha^n 
dde^'n Nga\. Tru+o+'c ddo' to^i mo+'i chi? ddu+o+.c nghe no'i ve^`  
nu+o+'c Nga vi~ dda.i, ddu+o+.c xem trie^?n la~m tha`nh tu+.u kinh 
te^' ky~ thua^.t cu?a Lie^n xo^ vo+'i nhu+~ng hi`nh ta^`u bay, ta^`u 
vu~ tru. o+? khu Trie^?n la~m Gia?ng vo~. DDo^'i vo+'i to^i lu'c 
ddo', nu+o+'c Nga la` nu+o+'c xa~ ho^.i chu? nghi~a pha't trie^?n, 
la` ddi?nh cao cu?a va(n minh nha^n loa.i, la` tha`nh tri` cu?a ho`a 
bi`nh, no'i to'm la.i la` thie^n ddu+o+`ng. Ngu+o+`i ta da.y va` 
tuye^n truye^`n cho to^i nhu+ va^.y ma`.

Ra kho?i cu+?a ha?i quan, Co^ Si'nh go.i ddie^.n cho DDa.i Su+'  
Qua'n. Ho+n mo^.t tie^'ng sau, mo^.t chie^'c xe cu?a Su+' qua'n ra 
sa^n bay ddo'n ddoa`n ve^` Nha` kha'ch Su+' qua'n o+? ga^`n be^'n  
metro Fruze\. Tre^n ddu+o+`ng tu+` sa^n bay ve^` nha` kha'ch dda~ co' 
the^? chie^m ngu+o+~ng su+. vi~ dda.i cu?a nu+o+'c Nga: nhu+~ng 
ru+`ng ba.ch du+o+ng ba.t nga`n, ro^`i dde^'n nhu+~ng da~y nha` cao 
nga^'t tro+`i ma` ddo+`i to^i chu+a ddu+o+.c tha^'y bao gio+`. Khi  
ho.c pho^? tho^ng, co' ba`i ho.c la` Ha` no^.i xanh (nhie^`u ca^y 
xanh) va`o loa.i nha^'t the^' gio+'i, nhu+ng sang Moscow mo+'i tha^'y 
the^' na`o la` xanh. Ha` no^.i nga`y xu+a co' le~ cu~ng xanh tha^.t, 
nhu+ng sau na`y ca^y co^'i bi. cha(.t ga^`n he^'t dde^? la^'y dda^'t 
xa^y nha` ro^`i\.

Ve^` dde^'n nha` kha'ch, ta^'t ca? ddoa`n ddu+o+.c pha^n va`o o+?  
chung mo^.t ca(n ho^. ba pho`ng. Tha^`y Quy`nh cu`ng sa'u ho.c sinh 
chia nhau hai pho`ng to (mo^~i pho`ng ke^ ddu+o+.c bo^'n giu+o+`ng 
xi't nhau), co`n co^ Si'nh o+? trong mo^.t pho`ng nho?  tru+o+'c 
ddu+o+.c du`ng la`m nha` kho\. Xe^'p xong ddo^` dda.c va` ta('m ru+?a 
xong, ma^'y ddu+'a ru? nhau ddi da.o cho+i ngay la^.p tu+'c, kho^ng 
he^` tha^'y me^.t mo?i gi` sau mu+o+`i ma^'y tie^'ng ddi ma'y bay\.  
Co`n co^ Si'nh tru+o+'c khi na(`m nghi? da(.n do` ma^'y anh "nha` 
que^ ra ti?nh" kho^ng ddu+o+.c ngo^`i da^~m cha^n le^n be^. ho^' xi', 
vi` co' the^? bi. vo+~ be^. nhu+ dda~ tu+`ng xa?y ra vo+'i mo^.t 
chi.; chi. na`y bi. ma?nh vo+~ dda^m va`o mo^ng, pha?i mang ddi ca^'p 
cu+'u\.

O+? nha` kha'ch, co^ Si'nh pha?i lo nhie^`u chuye^.n gia^'y to+` va` 
ve' ddi Helsinki vo+'i su+' qua'n co`n tha^`y Quy`nh cha(m so'c ca'c 
ho.c sinh tru+.c tie^'p ca? ma(.t toa'n la^~n ma(.t a(n uo^'ng. 
Tha^`y ra^'t hie^`n va` a^n ca^`n, va` ca'c ca^u chuye^.n ve^` toa'n 
cu?a tha^`y cu~ng ra^'t ha^'p da^~n. To^i co`n nho+' ddu+o+.c tha^`y 
gia?i thi'ch cho "hi`nh ca^`u co' su+`ng" cu?a Alexandrov. Tha^`y 
tru+o+'c tu+`ng la`m thu+.c ta^.p sinh o+? MGU (Moscow State  
University) ne^n tha.o tie^'ng Nga va` quen ca'ch so^'ng o+?  Moscow. 
Sa'ng so+'m ti?nh da^.y, tha^`y ru? mo^.t te^n na`o ddo' ddi mua 
ba'nh mi` va` bo+ su+~a ve^` cho ca? ddoa`n a(n sa'ng.  La^n dda^`u 
tie^n to^i ddu+o+.c bie^'t the^' na`o la` ba'nh mi` bo+ va` su+~a 
tu+o+i, sao ma` ngon the^'. Cha? tra'ch ngu+o+`i Nga ddu+o+.c a(n 
nhie^`u bo+ su+~a, tro^ng ai cu~ng to cao\.

Sau khi a(n sa'ng, sa'u te^n pha?i mang ba`i vo+? ra o^n luye^.n  
mo^.t lu'c, ro^`i ddu+o+.c ddi cho+i\. Anh ba.n co' ngu+o+`i nha` o+?  
Nga thu+o+`ng ddi cho+i rie^ng vo+'i ngu+o+`i nha`, chi? co' na(m  
te^n co`n la.i ddi cu`ng nhau\. Tha('ng ca?nh dda^`u tie^n la` co^ng 
vie^n ga^`n nha` kha'ch. Ra ddo' ddu+o+.c nha^.n ngay mo^.t cu'  
so^'c: hai co^ ca^.u ngu+o+`i Nga qua~ng 14-15 tuo^?i ddang ngo^`i 
tre^n ghe^' dda' ho^n nhau\. Tru+o+'c ddo' to^i ra^'t so+. ba.n  
ga'i, va` bi. ai ga'n ghe'p che^u tro.c thi` gia^.n la('m. Tu+` sau 
cu' so^'c na`y mo+'i na^?y no+? nhu+~ng y' nghi~ mo+ mo^.ng. Nhu+ng 
o+? Vie^.t nam ho^`i ddo' la`m gi` co' gia'o du.c ti`nh du.c, gia 
ddi`nh va` nha` tru+o+`ng dde^`u phe^ pha'n ki.ch lie^.t chuye^.n 
ye^u ddu+o+ng, va` ca'c tu+ tu+o+?ng kha('t khe ve^`  ti`nh ye^u va` 
ti`nh du.c cu~ng dda~ tha^'m va`o to^i nhu+ tho^i mie^n.

Ma^'y thu+' ddo^`ng ho^` a'o pho^ng ma` chu'ng to^i ddem sang Nga  
chu+a ki.p ho?i ba'n o+? dda^u, thi` dda~ ga(.p mo^.t anh kho^ng quen 
kho^ng bie^'t dde^'n ho?i mua\. Ho'a ra nha` kha'ch cu~ng la` cho^~ 
buo^n ba'n nho^.n nhi.p cu?a "da^n ta" tho+`i ddo'. To^i mang ca'c 
thu+' mi`nh co' ra ba'n, ddu+o+.c to^?ng co^.ng tre^n bo^'n chu.c 
ru'p, xem ra ca? mo^.t gia ta`i\. Mo^.t hai ho^m sau co' ma^'y anh 
ho.c khoa toa'n MGU, tru+o+'c cu~ng tu+`ng ddi thi toa'n quo^'c te^', 
ra tha(m chu'ng to^i\. Trong ddo' co' mo^.t anh ddi mo^.t ddo^i 
gia^`y ha' mo~m, ma^'y ddu+'a tha^'y ky` nhu+ng kho^ng da'm ba`n 
lua^.n. Anh Du~ng thi` ke'o theo luo^n ca? ma^'y chi. ho.c cu`ng na(m 
ra tha(m, tha^.t vui ve?. Ca'c anh chi. ru? chu'ng to^i ddi cho+i 
Moscow, chu.p a?nh ky? nie^.m, v.v.  To^i tho^? lo^. co' bo^'n chu.c 
ru'p va` muo^'n mua mo^.t ca'i ma'y a?nh, nhu+ng kho^ng co' ca'i ma'y 
a?nh na`o gia' bo^'n chu.c ru'p tru+` ma'y tre? con chu.p ra^'t xa^'u 
kho^ng ddie^`u chi?nh ddu+o+.c, ne^n dda`nh tho^i\. Bu` la.i, ca'c 
anh chi. mua ho^. cho mo^.t ca'i ba`n la` 7 ru'p la`m qua` ta(.ng 
me.. Ba`n la` Lie^n xo^ o+? Vie^.t nam tho+`i ddo' qui' la('m; ngay 
nhie^`u na(m sau mo^.t ngu+o+`i chi. ho. cu?a to^i so^'ng o+? tho^n 
que^ khi tha^'y to^i ddu+o+.c ddi "tu+ bo^?n" chi? ba`y to? nguye^.n 
vo.ng muo^'n ca^.u em ta(.ng ddu'ng mo^.t ca'i ba`n la` nhu+ va^.y\. 
Mua ba`n la` ro^`i, so^' tie^`n co`n la.i mua ke.o ba'nh va` nhu+~ng 
gi` to^i cu~ng cha(?ng nho+' nu+~a\. Chi? nho+' mo^.t la^`n na(m te^n 
ru? nhau va`o cu+?a ha`ng mua ke.o, khi ddi ra mo^.t lu'c ro^`i ti'nh 
la.i mo+'i tha^'y bi.  tra? thu+`a ma^'t qua~ng 4 ru'p, pha?i quay 
la.i xin la.i tie^`n. Cu+' nghi~ dde^'n chuye^.n ddo' la.i tha^'y 
ho+i ngu+o+.ng. Na(m te^n mang danh ddi thi toa'n quo^'c te^', ma` 
cu`ng nhau la`m sai mo^.t phe'p ti'nh co^.ng ddo+n gia?n.

Sau qua~ng ho+n mo^.t tua^`n o+? Moscow, chu'ng to^i le^n ta`u ho?a   
ddi Helsinki\. Ra dde^'n bie^n gio+'i, ha?i quan Nga cho ddo^?i mo^.t 
i't ru'p tha`nh tie^`n Pha^`n lan theo gia' ho^'i ddoa'i cu?a Nga, 
ti'nh ra mo^~i ngu+o+`i ddu+o+.c qua~ng hai chu.c ddo^`ng tie^`n 
Pha^`n lan. So^' tie^`n ddo^?i ddu+o+.c ddo' la` toa`n bo^. so^' 
tie^`n ngoa.i te^. ma` ddoa`n se~ co' khi o+? Pha^`n lan, co`n khi 
tu+` Vie^.t nam ddi hay khi o+? Moscow ddoa`n kho^ng ddu+o+.c ca^'p 
ddo^`ng ngoa.i te^. chuye^?n ddo^?i ddu+o+.c na`o, va` o+? Pha^`n lan 
kho^ng he^` co' DDa.i su+' qua'n hay La~nh su+. qua'n cu?a Vie^.t 
nam. Co^ Si'nh lo la('m. Co^ ra^'t so+. nho+~ co' chuye^.n gi` kho^ng 
may xa?y ra, cha(?ng ha.n nhu+ co' ai ddo' nho+~ tay dda'nh vo+~ 
cu+?a ki'nh, thi` la^'y dda^u ra tie^`n ma` dde^`n. Co^ be`n quye^'t 
ddi.nh ta.m giu+~ he^'t so^' tie^`n ma` chu'ng to^i ddo^?i ddu+o+.c 
dde^? dde^` pho`ng ba^'t tra('c.

Ta`u dde^'n sa^n ga dda~ co' ngu+o+`i ca^`m bie^?n ddo+.i ddo'n. DDo'  
la` mo^.t co^ ga'i Pha^`n lan to'c va`ng, da'ng ngu+o+`i dong do?ng 
cao, ma(.t ho+i co' la^'m cha^'m ta`m nhang, va` tro^ng ra^'t de^~  
thu+o+ng. Ra^'t tie^'c la` to^i dda~ que^n te^n co^. Co^ lu'c ddo' 
qua~ng 19 tuo^?i, la` sinh vie^n ngoa.i ngu+~, bie^'t no'i tha.o 
tie^'ng Anh, tie^'ng Pha'p va` bie^'t ca? mo^.t i't tie^'ng Nga\. Co^ 
ddi la`m the^m trong di.p he`, va` co^ng vie^.c cu?a co^ la` la`m 
hu+o+'ng da^~n, phie^n di.ch cho ddoa`n Vie^.t nam. Co^ Si'nh va` 
tha^`y Quy`nh co' the^? no'i chuye^.n vo+'i co^ phie^n di.ch ba(`ng 
tie^'ng Pha'p mo^.t ca'ch thoa?i ma'i\. Co^ Si'nh tru+o+'c la` Vie^.t 
kie^`u o+? Pha'p ne^n tie^'ng Pha'p cu?a co^ cha('c kho^ng ke'm gi` 
tie^'ng Vie^.t, co`n tha^`y Quy`nh cu~ng tu+`ng ddu+o+.c ddi thu+.c 
ta^.p o+?  Pha'p chi'n tha'ng theo tha^`y ke^?. Xem ra ddo' cu~ng la` 
ddie^`u may ma('n cho chu'ng to^i, ne^'u nho+' la.i nhu+~ng na(m 
tru+o+'c co' la^`n tha^`y Cha^u (o^ng Le^ Ha?i Cha^u) o+? Bo^. Gia'o  
Du.c da^~n ddoa`n Vie^.t nam ddi thi toa'n quo^'c te^', dde^'n khi 
di.ch dde^` thi tu+` tie^'ng Pha'p ra tie^'ng Vie^.t thi` di.ch sai  
dde^` mo^.t ba`i, la`m ho.c sinh Vie^.t nam kho^ng gia?i ddu+o+.c 
ba`i ddo'.

Bo.n ho.c sinh chu'ng to^i ddi theo co^ phie^n di.ch nhu+ng cu+'  
nhu+ bi. ca^m. Chi? co' anh Quye^`n la` bie^'t tie^'ng Anh co`n no'i 
chuye^.n ddu+o+.c vo+'i co^. DDe^'n mo^.t cho^~ ba'n kem, co^ gio+'i 
thie^.u kem Pha^`n lan ngon la('m va` ho?i chu'ng to^i co' muo^'n a(n 
kho^ng. Ca? bo.n the`m ro? gia~i nhu+ng kho^ng co' xu na`o ne^n pha?i 
no'i gia? vo+` "O+? dda^y la.nh la('m, chu'ng to^i kho^ng muo^'n 
a(n". Ma^'y ho^m sau, khi ddu+o+.c ddi tha(m quan mo^.t nha` ma'y 
su+~a cu?a Pha^`n lan va` ddu+o+.c mo+`i a(n kem kho^ng ma^'t tie^`n, 
ma^'y te^n mo+'i tranh nhau a(n. A^'n tu+o+.ng dde^? la.i la` kem 
Pha^`n lan ngon vo^ cu`ng, ngon ho+n ha(?n ca'c loa.i kem to^i 
ddu+o+.c a(n o+? Vie^.t nam hay o+? Nga\. Ve^` sau sang Y' ddu+o+.c 
a(n nhie^`u kem Y', va` mo.i ngu+o+`i thu+o+`ng hay khen la` kem Y' 
ngon nha^'t the^' gio+'i, nhu+ng to^i kho^ng tha^'y ca'i kem na`o 
ngon ba(`ng ca'i kem a(n o+? Pha^`n lan. Kho^ng hie^?u ba^y gio+` 
ne^'u ddu+o+.c a(n la.i kem Pha^`n lan se~ co`n tha^'y ngon nhu+ 
tru+o+'c nu+~a kho^ng.

Tu+` Helsinki, chu'ng to^i ddu+o+.c chuye^?n dde^'n mo^.t khu du  
li.ch na`o ddo' be^n bo+` mo^.t ca'i ho^` lo+'n. Tru+o+'c ddo' cu~ng 
ki.p tha(m quan qua tha`nh pho^'. Helsinki tro^ng kha' de^~ thu+o+ng, 
vo+'i nhu+~ng ngo^i nha` xinh xa('n ma^`u na^u sa'ng kho^ng to la('m, 
vo+'i nhu+~ng chie^'c thuye^`n buo^`m dda^.u sa't nhau be^n bo+` 
ho^`. Ma` Pha^`n lan la` dda^'t nu+o+'c cu?a ho^`, ddi dda^u cu~ng 
tha^'y toa`n ho^` la` ho^`. Sa'u ho.c sinh Vie^.t nam ddu+o+.c cho  
o+? trong mo^.t ca(n ho^. kha'ch sa.n trong mo^.t da~y nha` mo^.t 
ta^`ng be^n bo+` ho^`, ca.nh ho.c sinh ca'c nu+o+'c ca'c. Nhu+~ng  
ngu+o+`i tru+o+?ng pho' ddoa`n thi` o+? cho^~ kha'c ga^`n ddo'. Ca(n 
ho^.  chu'ng to^i ddu+o+.c pha^n tro^ng ra^'t li.ch su+., nhu+ng la.i 
thie^'u giu+o+`ng, chi? co' 4 giu+o+`ng ddo+n. Tha^`y Quy`nh hay co^ 
Si'nh no'i la` dda^`u tie^n ngu+o+`i ta ddi.nh pha^n bo+'t mo^.t  
so^' trong so^' 6 ho.c sinh Vie^.t nam sang ca(n ho^. kha'c nhu+ng 
sau la.i tho^i\. Vi` sao thi` to^i kho^ng bie^'t. Trong pho`ng  
kha'ch cu?a ca(n ho^. co' mo^.t ca'i ghe^' da`i, ke'o ra ddu+o+.c 
mo^.t ca'i giu+o+`ng ddo+n, tha`nh 5 ca'i to^?ng co^.ng, va^~n 
thie^'u mo^.t ca'i\. Bo.n to^i pha?i pha^n ba te^n ngu? chung nhau 
hai giu+o+`ng ddo+n ghe'p la.i tha`nh mo^.t giu+o+`ng ddo^i\. Kho^ng 
hie^?u ca'c ho.c sinh ca'c nu+o+'c kha'c thi` ddu+o+.c ngu? the^' 
na`o\.  Ne^'u ho. bie^'t ba te^n Vie^.t nam ngu? chung mo^.t 
giu+o+`ng ddo^i thi` cha('c la` buo^`n cu+o+`i la('m, tu+o+?ng bo.n 
na`y ddo^`ng ti'nh luye^'n a'i\.

Trong ca(n ho^. kha'ch sa.n co' ca? vo^ tuye^'n ma^`u va` ddie^.n  
thoa.i, la` nhu+~ng thu+' ma` tru+o+'c dda^y ha~n hu+~u to^i mo+'i 
"ddu+o+.c nhi`n chu+' kho^ng ddu+o+.c so+`". Thu+? ba^.t vo^  tuye^'n 
le^n xem, tha^'y ddang chie^'u phim truye^.n gi` quen quen hi`nh nhu+ 
dda~ tu+`ng ddu+o+.c xem tru+o+'c ddo', tuy lo+`i thi` kho^ng hie^?u 
vi` ba(`ng tie^'ng Pha^`n lan. Nhu+ng cu+' xem ddu+o+.c qua~ng 5 
phu't la.i co' mo^.t tra`ng qua?ng ca'o da`i, cha'n qua' dda`nh  bo? 
kho^ng ddoa'i hoa`i dde^'n TV nu+~a\. DDie^.n thoa.i cu~ng muo^'n 
thu+? so+` mo', co' mo^~i mo^.t ca'ch la` go.i ddie^.n cho tha^`y  
Quy`nh hoa(.c co^ Si'nh, kho^ng ma^'t tie^`n vi` trong cu`ng khu du 
li.ch. O^ng Ta^y o+? cu`ng pho`ng vo+'i tha^`y Quy`nh ho^m dda^`u  
pha?i nha^.n xe't "Bo.n ho.c sinh cu?a o^ng sao hay go.i ddie^.n cho 
o^ng the^'".

Cu+?a sau cu?a ca(n ho^. kha'ch sa.n mo+? ngay ra bo+` ho^`. Ho^m  
dda^`u, chu'ng to^i nhi`n tha^'y co' mo^.t ca'i thuye^`n go^~ bo?  
tro^'ng, nghi~ thuye^`n tu+. do ai muo^'n ddi thi` ddi, be`n ha(m  
ho+? xo^ng le^n che`o thuye^`n da.o quanh ho^`. DDang che`o cho+i 
thi` tha^'y mo^.t anh ba.n nu+o+'c ngoa`i lo+?n vo+?n o+? bo+`  ho^`, 
be`n ra ba('t chuye^.n, anh Quye^`n la`m phie^n di.ch tie^'ng Anh.  
Tro^ng anh ra^'t tre? ne^n chu'ng to^i tu+o+?ng cu~ng la` ho.c  sinh 
ddi thi, ho?i ra mo+'i bie^'t anh tru+o+'c dda^y cu~ng tu+`ng ddi thi 
toa'n olympic, nhu+ng la^`n na`y da^~n ddoa`n Balan ddi thi\. To^i  
tha^'y ra^'t hay, va` cho+.t nghi~ ne^'u sau na`y mi`nh co' di.p 
da^~n ddoa`n Vie^.t nam ddi thi thi` cu~ng vui bie^'t ma^'y\. Ho^m  
sau ddu+o+.c co^ phie^n di.ch no'i cho bie^'t muo^'n che`o thuye^`n 
pha?i thue^, the^' la` ti.t luo^n khoa?n thuye^`n.

Khoa?n la`m quen vo+'i ca'c ba.n the^' gio+'i cu~ng ta^.m ti.t, chu? 
ye^'u do ngo^n ngu+~ ba^'t ddo^`ng. Mo^.t la^`n ddi.nh la`m quen 
vo+'i ca'c ba.n o+? ddoa`n Lie^n xo^ anh em, nhu+ng ra(.n ma~i  mo+'i 
ra ddu+o+.c ma^'y ca^u cha`o tie^'ng Nga, va` ca'c ba.n na`y cu~ng 
kho^ng co' ve? nhie^.t ti`nh ddo^'i dda'p la.i, kho^ng hie^?u co' 
pha?i ta.i coi thu+o+`ng ma^'y anh Vie^.t nam kho^ng. Tui kho^ng no'i 
chuye^.n ddu+o+.c gi` ma^'y vo+'i ba.n be` na(m cha^u, nhu+ng bo.n 
to^i cu~ng ddu+o+.c ca'c ba.n ta(.ng mo^.t i't qua` linh tinh la`m 
ky? nie^.m, trong ddo' co' huy hie^.u, co+` qua.t va` mo^.t ddo^'ng 
sa'ch ddu? ca'c loa.i chu+~ ngoa(`n nghe`o\. DDo' la` ca'c sa'ch 
toa'n pho^? tho^ng da`nh cho ho.c sinh ye^u toa'n cu?a ca'c nu+o+'c 
kha'c nhau\. Co^ Si'nh va` tha^`y Quy`nh cu~ng ddu+o+.c ta(.ng 
nhie^`u sa'ch kie^?u va^.y, va` cho la.i bo.n to^i vi` hai tha^`y co^ 
dde^`u la` gia'o su+ dda.i ho.c kho^ng quan ta^m dde^'n toa'n pho^? 
tho^ng. To^i sau ky` thi ve^` nu+o+'c cu~ng se~ ta(.ng la.i toa`n 
bo^. so^' sa'ch vo+? ho.c toa'n pho^? tho^ng cu?a mi`nh cho kho^'i 
chuye^n toa'n To^?ng ho+.p va` cho nhu+~ng ai to^i kho^ng nho+' 
nu+~a\. Chi? nho+' mo^.t chuye^.n tu+o+ng pha?n sau:  Co' la^`n co^ 
Sinh cu`ng tha^`y Cha^u da^~n ddoa`n ddi thi toa'n olympic o+? dda^u 
ddo', cu~ng ddu+o+.c ca'c nu+o+'c ta(.ng mo^~i ngu+o+`i mo^.t so^' 
sa'ch toa'n pho^? tho^ng. Co^ Si'nh kho^ng ca^`n du`ng ne^n cho la.i 
ca'c ho.c sinh. Tha^`y Cha^u tha^'y the^' be`n thu la.i dde^? kho?i 
"lo^. bi' ma^.t". Cha(?ng qua la` do tha^`y muo^'n "giu+~ tu?", dde^? 
tha^`y co`n in sa'ch va` luye^.n thi\. Xung quanh tha^`y Cha^u co`n 
nhie^`u chuye^.n kho^ng hay kha'c, ma` nhu+~ng ngu+o+`i dda~ tham gia 
thi toa'n olympic tru+o+'c sau bo.n to^i i't na(m cha('c dde^`u nghe 
no'i\.

Trong so^' ca'c ba.n na(m cha^u, co' mo^.t ba.n ho'a ra la.i la`  
ngu+o+`i Vie^.t nam, mo+'i ddi di ta?n i't la^u, va` la^`n ddo' ddi 
thi toa'n olympic cho ddo^.i Canada (ne^'u to^i nho+' kho^ng nha^`m). 
Anh ba.n na`y ma(.c mo^.t bo^. com le^ sang tro.ng, cu'c to?a a'nh 
va`ng la^'p la'nh, do chi'nh phu? may cho\. To^i nhi`n la.i chie^'c 
a'o ve't cu~ ma^`u choi cho'i, chie^'c gia^`y gia^'y tre^n ngu+o+`i 
mi`nh ma` ho+i tu?i\. Chu'ng to^i co' ddi cho+i va` chu.p a?nh cu`ng 
nhau vo+'i anh ba.n Vie^.t kie^`u na`y, nhu+ng ra^'t tie^'c kho^ng 
hie^?u sao to^i kho^ng co' ta^'m a?nh na`o ca?, cu~ng kho^ng giu+~ 
lie^n la.c vo+'i anh, va` ba^y gio+` cu~ng kho^ng nho+' te^n anh ba.n 
na`y la` gi`. Qua? dda^'t tro`n, bie^'t dda^u se~ la.i co' lu'c ga(.p 
la.i anh ta\.

Ky` thi olympic ke'o da`i ho+n chu.c ho^m, nhu+ng chi? co' hai  ho^m 
thi, co`n la.i la` a(n va` cho+i, sung su+o+'ng nhu+ ddi nghi? he` 
o+? no+i sang tro.ng va^.y, ne^'u que^n ddi chuye^.n kho^ng co' mo^.t 
xu di'nh tu'i\. A(n uo^'ng thi` o+? kha'ch sa.n ngay trong khu du 
li.ch. A(n kie^?u Ta^y, co' kha(n lo't ddu`i, co' dao co' di~a pha?i 
ba('t chie^'c thie^n ha. ca^`m sao cho ddu'ng kie^?u\. To^'i dde^'n 
co' nha^?y disco o+? mo^.t gian ro^.ng, ddo^ng ddu'c ngu+o+`i tham 
du+.. Bo.n to^i cha(?ng ddu+'a na`o bie^'t nha^?y, nhu+ng to^'i to^'i 
va^~n ru? nhau ddi nghe nha.c chay, kho^ng nha?y cu~ng cha(?ng uo^'ng 
chi, mo^.t lu'c ro^`i ddi ve^`. Ha`ng nga`y co' xe buy't cho+? ddi 
tha(m quan ca'c no+i\. Sa'ng ra cu+' vie^.c ngo^`i le^n xe buy't 
ddo+.i sa(~n, ne^'u ddi cho+i qua' tru+a thi` ddi dde^'n dda^u 
ddu+o+.c a(n o+? dda^'y\. Ban to^? chu+'c co' ve? ra^'t chu' tro.ng 
cho bo.n to^i ddi cho+i, tha(m quan nhie^`u no+i kha'c nhau\. La^`n 
thi` ddi tha(m quan nha` ma'y su+~a\. Ngu+o+`i ta khoe co' nhu+~ng 
ddu+o+`ng o^'ng su+~a dde^? chuye^?n tha(?ng su+~a tu+` no+i nuo^i 
bo` dde^'n nha` ma'y, ro^`i khoe ca'c vo? ho^.p su+~a du`ng o+? Lie^n 
xo^ la` nha^.p tu+` Pha^`n lan. (Pha^`n lan a('t ha(?n ddu+o+.c "a(n 
lo^.c" Lie^n xo^ cu~ nhie^`u la('m, vi` khi Lie^n xo^ cu~ tan gia~ 
thi` ty? le^. tha^'t nghie^.p cu?a Pha^`n lan se~ ta(ng vo.t le^n 
tha`nh 18%). Co' la^`n xe buy't cho+? ddi tha(m mo^.t nha` ma'y sa?n 
xua^'t bu't, mo^~i ngu+o+`i dde^'n tha(m ddu+o+.c ta(.ng mo^.t ca'i 
bu't bi co' ke`m ddo^`ng ho^` ddie^.n tu+? o+? tha^n bu't, tro^ng 
mo+'i hie^.n dda.i qui' gia' la`m sao\. La^`n kha'c, mo.i ngu+o+`i 
ddu+o+.c cho+? dde^'n mo^.t cho^~ co' the^? ta('m ho+i, mo^.t trong 
nhu+~ng "mo'n truye^`n tho^'ng" cu?a Pha^`n lan. Co^ phie^n di.ch 
ha(m ho+?  ddi va(.t ca'c ca`nh la' gi` ddo' dde^? qua^.t va`o 
ngu+o+`i khi ta('m. To^i thi` bi. be^.nh ba?o thu?, chu+a ddu+o+.c 
ta('m ho+i bao gio+`, nghe no'i dda~ tha^'y nga.i, ne^n kho^ng va`o 
thu+?.

Mo^.t la^`n, ngu+o+`i ta cho+? ca'c ddoa`n ddi dde^'n mo^.t ho`n  
dda?o, va` a(n to^'i luo^n o+? ddo' vo+'i mo'n a(n chi'nh la` ca'. 
Tre^n  dda?o co' mo^.t tro` cho+i kha' dda(.c bie^.t: Mo^.t ca^y go^~ 
tro`n dda(.t ngang o+? vi. tri' cao khoa?ng 1 me't. Hai ngu+o+`i 
ngo^`i hai dda^`u ca^y go^~, mo^~i ngu+o+`i ca^`m mo^.t ca'i bao ta?i 
to ddu+.ng gi` ddo' kha' nhe. (cha('c la` ro+m), va` du`ng bao ta?i 
qua^.t nhau\. Ai ma^'t tha(ng ba(`ng bi. nga~ thi` thua mo^.t 
ddie^?m. Tro` dda^'u bao ta?i na`y kha' ha^'p da^~n, va` mo^.t cuo^.c 
thi dda^'u loa.i tru+.c tie^'p giu+~a ca'c nu+o+'c ddu+o+.c to^? 
chu+'c, mo^~i nu+o+'c cho.n mo^.t ngu+o+`i ra dda^'u\.  Lua^.t dda^'u 
la` trong mo^~i tra^.n, ai tha('ng ddu+o+.c hai ddie^?m thi` tha('ng. 
To^i to xa'c nha^'t ddoa`n Vie^.t nam ne^n ddu+o+.c ca'c ba.n cho ra 
thi dda^'u\. Vo`ng dda^`u ga(.p ngay anh ba.n ngu+o+`i My~. Ly' do 
ra^'t ddo+n gia?n: khi xe^'p thu+' tu+. ABC ca'c nu+o+'c tham gia thi 
toa'n, VN va` USA ddu+'ng sa't nhau\. Lu'c dda^'u vo+'i anh My~, ca'c 
ba.n be` the^' gio+'i ddu+'ng vo`ng trong vo`ng ngoa`i dde^? xem, va` 
kho^ng ngu+`ng ho^ "Vietnam, Vietnam" dde^? co^? vo~, co`n kho^ng 
tha^'y ai ho^ My~. Ra^'t ca?m ddo^.ng khi tha^'y ca'c ba.n qui' me^'n 
Vietnam dde^'n chu+`ng na`o\. Ca' tra^.n giu+~a ca'c nu+o+'c kha'c  
kho^ng co' tra^.n na`o ddu+o+.c co^? vu~ nhu+ va^.y\. Sau i't gia^y, 
anh My~ phang tru'ng to^i mo^.t qua? la(n quay ngu+o+`i xuo^'ng  
du+o+'i ca^y go^~, the^' la` thua mo^.t ddie^?m. La.i nha?y le^n ca^y 
go^~. Anh My~ la.i phang pha?i to^i mo^.t qua? nu+~a, suy't thua  
ha(?n. May thay la^`n na`y to^i cu~ng ki.p phang la.i va`o ngu+o+`i 
anh My~ tru+o+'c khi nga~. The^' la` ca? hai cu`ng nga~ mo^.t lu'c, 
kho^ng ti'nh ddie^?m. La.i dda^'u tie^'p. La^`n na`y dde^'n lu+o+.t 
to^i vo+`n anh My~ ro^`i phang cho anh mo^.t qua? va`o cha^n, la`m 
anh ma^'t tha(ng ba(`ng nga~ quay xuo^'ng. Mo.i ngu+o+`i co^~ vu~ 
la.i ca`ng ho^ ha`o to to+.n. Phen cuo^'i cu`ng, to^i la^'y su+'c 
tha^.t ma.nh phang bao ta?i va`o vai anh My~.  The^' la` chie^'n 
tha('ng trong tie^'ng hoan ho^ ra^`m ro^.! Theo anh Quy`nh ke^?, co' 
mo^.t anh ngu+o+`i Anh, ddi sang Pha^`n lan cho+i nha^n di.p em cu?a 
anh ta ddi thi, sau ddo' co`n say ru+o+.u va` la(.p ddi la(.p la.i 
ca^u no'i "Vie^.t nam tha('ng My~".  Vo`ng hai ti`nh co+` to^i 
ddu+o+.c mie^~n vi` so^' ngu+o+`i va`o vo`ng hai le?. Va`o dde^'n 
vo`ng 3, ga(.p ngay mo^.t anh ngu+o+`i dda?o Cypres, be'o lu`n cha('c 
ni.ch tro^ng pha?i dde^'n mo^.t ta.. La^`n na`y kha'n gia? cu~ng 
ddo^`ng thanh ho^ "Vietnam, Vietnam" lie^n tu.c. Nhu+ng to^i vu+`a 
dda(.t mo^ng le^n tre^n ca^y go^~, chu+a ki.p chi?nh vi. tri' ngo^`i, 
thi` anh ba.n ngu+o+`i Cypres kho^ng ca^`n ddo+.i gi` dda~ phang cho 
ngay mo^.t qua? la(n xuo^'ng. Le^n la.i ca^y go^~, nhu+ng chu+a ki.p 
ngo^`i cho tha(ng ba(`ng anh dda?o Cypres dda~ phang tie^'p ngay cho 
qua? kha'c, the^' la` xong, cha? bie^'t no'i the^' na`o\. Ma^'y anh 
cha`ng dda?o Cypres lu'c ddo' mo+'i "da'm" ho^ hoa'n. Va`o vo`ng  
trong, anh ngu+o+`i Cypres na`y se~ la.i thua mo^.t anh ngu+o+`i 
Nga\.

Va`o hai ho^m thi, chu'ng to^i ddu+o+.c cho+? dde^'n mo^.t tru+o+`ng  
tie^?u ho.c ddang nghi? he`, no+i mo^~i ho.c sinh se~ ddu+o+.c cho 
ngo^`i tru+o+'c mo^.t ba`n nho? dde^? la`m  ba`i thi\. DDe^` ba`i  
dda~ ddu+o+.c ca'c tru+o+?ng, pho' ddoa`n di.ch ra tie^'ng ca'c 
nu+o+'c du+. thi\.  Khi la`m ba`i thi, ho.c sinh nu+o+'c na`o cu+' 
vie^.c la`m ba`i ba(`ng tie^'ng nu+o+'c dda^'y, ca'c tru+o+?ng pho' 
ddoa`n se~ la.i la`m phie^n di.ch, di.ch ra mo^.t trong ca'c thu+' 
tie^'ng quo^'c te^' nhu+ Anh, Pha'p, Ta^y ban nha, dde^? ban gia'm 
kha?o co' the^?  hie^?u ddu+o+.c. Ban gia'm kha?o cu~ng ddu+o+.c 
la^.p tha`nh tu+` chi'nh ca'c tru+o+?ng pho' ddoa`n, ngu+o+`i ddoa`n 
na`y thi` ddi cha^'m ba`i ddoa`n kha'c, va` thu+o+`ng dde^? cha^'m 
mo^.t ba`i co' 5-7 ngu+o+`i tu+` ca'c ddoa`n kha'c tham du+.. Trong 
ca'i tro` di.ch na`y co' the^? xa?y ra gian la^.n, vi` khi kho^ng co' 
ngu+o+`i na`o trong ban gia'm kha?o hie^?u tie^'ng ma` ho.c sinh la`m 
ba`i, thi` tru+o+?ng pho' ddoa`n co' the^? la'i di.ch sao cho ly' 
lua^.n cu?a ho.c sinh tu+` sai tha`nh ddu'ng. Ta^'t nhie^n gian la^.n 
kho^ng de^~, vi` cho^~ na`o nhie^`u co^ng thu+'c ra`nh ra`nh thi` 
kho^ng di.ch tra^.t ddu+o+.c, va` nhu+~ng ngu+o+`i gia'm kha?o cu~ng 
ho?i ra^'t ky~ tu+`ng tu+` mo^.t ho.c sinh vie^'t nghi~a la` gi`. Thi 
olympic ma` la.i gian la^.n thi` ma^'t ca? y' nghi~a, nhu+ng ai cu~ng 
thi'ch ddu+o+.c tha`nh ti'ch cao, ne^n gian la^.n va^~n xa?y ra\. Ca' 
bie^.t co' tru+o+`ng ho+.p lo^. dde^` thi olympic toa'n na(m na`o 
ddo' o+?  Ba('c Trie^`u tie^n. Nghe no'i nhu+~ng na(m tru+o+'c, 
ddoa`n Vie^.t nam cu~ng ddu+o+.c a(n the^m mo^.t va`i ddie^?m do 
kha^u di.ch thua^.t. DDu+o+.c ca'i na(m chu'ng to^i ddi thi, ddoa`n 
Vie^.t nam dda~ giu+~ ddu+o+.c su+. trung thu+.c, hay i't ra la` to^i 
ca?m tha^'y va^.y\.

Tu+o+ng tu+. nhu+ ca'c na(m kha'c, dde^` thi olympic na(m chu'ng to^i  
co' sa'u ba`i, mo^~i ho^m pha?i la`m 3 ba`i trong vo`ng bo^'n tie^'ng 
ru+o+~i (ne^'u to^i nho+' kho^ng nha^`m). Thu+o+`ng mo^~i ho^m co' 
hai ba`i de^~, mo^.t ba`i kho'. De^~ hay kho' cu~ng co`n tu`y 
"tru+o+`ng pha'i". DDo^'i vo+'i to^i co' 5 ba`i to^i la`m ngon o+ 
ha^`u nhu+ cha(?ng pha?i suy nghi~ gi`, nhu+ng co' mo^.t ba`i nghi~ 
ca? buo^?i kho^ng ra dda`nh chi.u\. Kho^ng chi.u ha(?n, vi` theo mo.i 
ngu+o+`i da(.n do` la` ne^'u kho^ng gia?i ddu+o+.c nhu+ng nghi~ ra 
gi` thi` cu+' vie^'t va`o, ne^n to^i cu~ng ne^.n va`o gia^'y la`m 
ba`i va`i suy lua^.n linh tinh va` the^m ca? mo^.t gia?  thuye^'t 
to^?ng qua't ho+n cho ba`i ddo'. Ma^'y ngu+o+`i trong ban gia'm kha?o 
khi cha^'m tha^'y gia? thuye^'t cu?a to^i cu~ng chi.u kho^ng bie^'t 
ddu'ng hay sai, ne^n cuo^'i cu`ng ho. quye^'t ddi.nh cho to^i ba`i 
ddo' 2 ddie^?m tre^n 7. Cu?a thie^n gia? ddi.a:  Co' mo^.t ba`i ve^` 
gia?i ti'ch, dda.i loa.i ve^` chuo^~i ho^.i tu. hay pha^n ky`, la` 
thu+' to^i ra^'t quen thuo^.c tho+`i ddo' va` la`m ngon o+. Nhu+ng do 
de^~ qua' ne^n que^n ma^'t la` ba`i co' hai ca^u ho?i, chi? vie^'t 
va`o gia^'y mo^~i mo^.t ca^u dda^`u, the^' la` la.i bi. tru+` phe'ng 
ddi 2 ddie^?m. Ke^'t qua? la` ddu+o+.c 7 X 5 = 35 ddie^?m tre^n 42.

Mo.i ngu+o+`i cho ra(`ng chi'nh ca'i ba`i ca? ddoa`n Vie^.t nam  
kho^ng ai gia?i ddu+o+.c la` ba`i kho' nha^'t ky` thi, vi` no' ra^'t 
mo+'i la., va` lie^n quan dde^'n tin ho.c, dde^'n tru+o+`ng dda 
thu+'c he^. co+ so^' 2, v.v. Nhu+ng ddo^'i vo+'i mo^.t so^' ba.n 
ngu+o+`i Nga hay ngu+o+`i Hungary thi` hi`nh nhu+ ba`i ddo' la.i la` 
ba`i de^~ vi` nhie^`u ngu+o+`i gia?i ddu+o+.c. Trong khi ddo' co' 
mo^.t ba`i hi`nh ho.c pha(?ng la` thu+' ma` ho.c sinh ca^'p hai cu?a 
Vie^.t nam cha('c cu~ng gia?i bay, thi` la.i kho' vo+'i ho.. Cao 
ddie^?m nha^'t ddoa`n Nga la.i la` mo^.t co^ ga'i, ddu+o+.c 36 
ddie^?m, chi'nh vi` kho^ng gia?i ddu+o+.c ba`i hi`nh ho.c pha(?ng. 
Ve^` sau tha^'y ba?o co^ na`y cu~ng se~ ho.c khoa toa'n MGU, nhu+ng 
to^i kho^ng ga(.p la.i bao gio+` (hay co' ga(.p la.i ma` kho^ng 
nha^.n ra).

DDe^` thi na(m bo.n to^i thuo^.c loa.i ho+i kho' ho+n ca'c na(m  
kha'c, tu+'c la` ddie^?m thi trung bi`nh ye^'u ho+n ca'c na(m kha'c, 
ne^n ban to^? chu+'c quye^'t ddi.nh 34 ddie^?m tro+? le^n dda~  
ddu+o+.c gia?i nha^'t (huy chu+o+ng va`ng).  The^' la` may ma('n to^i 
cu~ng ddu+o+.c lo.t va`o trong so^' nhu+~ng ngu+o+`i ddu+o+.c gia?i 
nha^'t. Coi nhu+ hoa`n tha`nh tra'ch nhie^.m, vi` tru+o+'c ddo' to^i 
ddu+o+.c coi la` kha' nha^'t ddoa`n Vie^.t nam, va` ma^'y tha^`y co' 
dda(.t hy vo.ng ddoa.t gia?i nha^'t va`o to^i\. Ke^'t qua cuo^'i 
cu`ng, Vie^.t nam co' na(m ngu+o+`i ddu+o+.c gia?i\. Nhu+ng vinh du+. 
nha^'t co' le~ la` na(m ddo' ddoa`n Vie^.t nam xe^'p thu+' 5, tre^n 
ddoa`n Lie^n xo^ xe^'p thu+' 6. Ho^m trao gia?i thu+o+?ng, dda^`u 
tie^n la` nhu+~ng ngu+o+`i gia?i nha^'t ddu+o+.c go.i le^n, xe^'p 
tha`nh mo^.t ha`ng. Khi ngu+o+`i ta go.i dde^'n te^n, to^i vo^.i 
ma(.c chie^'c a'o ve't ke^.ch co+~m va`o dde^? ddi le^n. Lu'c ddo' 
a'o dda~ bi. ddu+'t cu'c o+? co^? tay\.  Ngu+o+`i ta pha't cho to^i 
mo^.t ca'i ba(`ng, va` mo^.t ca'i huy chu+o+ng hi`nh tro`n ma`u va`ng 
xi?n kho^ng bie^'t ba(`ng cha^'t lie^.u gi`, ddu+.ng trong mo^.t ca'i 
ho^.p.  (Cu.c huy chu+o+ng ca^`m ho+i na(.ng na(.ng, cha('c gia 
ddi`nh to^i o+? Vie^.t nam hie^.n co`n giu+~. Gia' no' ba(`ng va`ng 
tha^.t, co' khi to^i dda~ ba'n qua'ch no' ddi dde^? trang tra?i no+. 
na^`n ddo+~ cho bo^' me. ro^`i). Ngu+o+`i ta co`n co' mo^.t i't ma'y 
ti'nh ca' nha^n la`m pha^`n thu+o+?ng, nhu+ng kho^ng hie^?u do 
thie^'u ma'y hay sao ne^n chi? thu+o+?ng cho nhu+~ng ngu+o+`i 
ddu+o+.c 36 ddie^?m tro+? le^n. The^' la` la.i ddu+o+.c the^m mo^.t 
di.p te~n to`, tu?i\.

Buo^?i pha't pha^`n thu+o+?ng hi`nh nhu+ cu~ng la` buo^?i chi'nh  
thu+'c cuo^'i cu`ng cu?a ky` thi\. Ho^m sau va` ho^m sau nu+~a ca'c 
ddoa`n se~ ru.c ri.ch ra ve^`. Co^ Si'nh go.i bo.n to^i la.i ho?i y' 
kie^'n: "So^' tie^`n ddo^?i ddu+o+.c khi qua be^n gio+'i Lie^n xo^ - 
Pha^`n lan va^~n co`n nguye^n, ca'c em co' ddo^`ng y' du`ng tie^`n  
ddo' dde^? dda'nh ddie^.n ve^` Vie^.t nam tho^ng ba'o ke^'t qua?  
kho^ng ?". Ca? bo.n ddo^`ng thanh tra? lo+`i "Kho^ng". The^' la` co^ 
tra? la.i tie^`n cho ca? bo.n, muo^'n tie^u gi` thi` tie^u\. Thu+.c 
ra thi` va`i ddo^`ng co?n coi cu~ng cha? mua ddu+o+.c gi`, ngoa`i  
va`i tranh a?nh, qua` ky? nie^.m re? tie^`n. Chi? kho^? cho ca'c vi.  
phu. huynh o+? Vie^.t nam, ha`ng nga`y le^n cu+?a Bo^. Gia'o Du.c  
ngo'ng ddo+.i tin cu?a ddoa`n ddi thi nhu+ng cha(?ng tha^'y gi` cho 
dde^'n ho^m ddoa`n quay ve^` la.i dde^'n Moscow.

Ve^` dde^'n Vie^.t nam, kho^ng co' tro^'ng ke`n gi`. Ca'c ba.n  
ngu+o+`i mie^`n Nam se~ co`n ddu+o+.c giu+~ o+? la.i Hanoi va`i ho^m 
dde^?  co' buo^?i ga(.p ma(.t tha^n ma^.t vo+'i mo^.t quan chu+'c 
na`o ddo' cu?a chi'nh phu?. Cuo^'i cu`ng thi` cu~ng cha? co' quan 
chu+'c na`o ngoa`i mo^.t o^ng Bo^. tru+o+?ng hay Thu+' tru+o+?ng Bo^. 
Gia'o du.c. Trong buo^?i ga(.p ma(.t ddo', Bo^. tuye^n du+o+ng tha`nh 
ti'ch cu?a chu'ng to^i, va` pha't pha^`n thu+o+?ng. "Pha^`n  
thu+o+?ng tinh tha^`n" kha' quan tro.ng: Chu'ng to^i ddu+o+.c dda(.c 
ca'ch to^'t nghie^.p pho^? tho^ng va` ddu+o+.c ddi ho.c nu+o+'c 
ngoa`i, mo+? dda^`u cho cuo^.c ddo+`i bo^n ba ha?i ngoa.i\. Thu+.c ra 
se~ chi? co' 4 trong so^' 6 ddu+'a se~ ra nu+o+'c ngoa`i ho.c. Mo^.t 
ba.n pha?i o+? la.i trong nu+o+'c vi` ly' do su+'c kho?e, co`n mo^.t 
ba.n kha'c do "tha`nh pha^`n ly' li.ch". Pha^`n thu+o+?ng va^.t 
cha^'t thi` ra^'t khie^m to^'n: to^i ddu+o+.c hai mie^'ng va?i, mo^~i 
mie^'ng ddu? may mo^.t ca'i qua^`n da`i\. Ca'c ba.n mie^`n Nam se~ 
co`n ddu+o+.c ca'c ti?nh trong ddo' thu+o+?ng tie^'p. Me. to^i nha^n 
di.p ddo' cu~ng se~ ddu+o+.c thu+o+?ng mo^.t ca'i cha^.u nho^m trong 
mo^.t ho^.i nghi. "Phu. nu+~ ba dda?m ddang". Ca'c ba'o chi' nha^n 
di.p ddo' se~ co' va`i ba`i bie^?u du+o+ng tha`nh ti'ch cu?a ho.c 
sinh Vie^.t nam, ro^`i nha^n tie^.n ma` bie^?u du+o+ng luo^n ne^`n 
toa'n ho.c Vie^.t nam. Nha^n da^n nha^n di.p ddo' se~ co' va`i 
chuye^.n ddo^`n dda.i ba^.y ba. ve^` ma^'y te^n ddi thi toa'n, tuy 
kho^ng so^i no^?i ba(`ng nhu+~ng su+. ddo^`n dda.i ve^` Le^ Ba' 
Kha'nh Tri`nh hay Le^ Tu+. Quo^'c Tha('ng. Va` se~ co' ma^'y ba.n 
ha^m mo^. toa'n vie^'t thu+ cho chu'ng to^i\. To^i ho^`i ddo' chu+a 
bie^'t vie^'t thu+ la` gi`, nha^.n ddu+o+.c thu+ kho^ng tra? lo+`i, 
sau na`y co`n a'i nga.i ve^` vie^.c la`m ba^'t nha~ na`y\.

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