program doixung;
uses crt;
var f,f1:text;
a:array[1..100] of longint;
n,i,dem:longint;
begin
assign(f,'so.inp');
assign(f1,'so.out');
reset(f);
readln(f,n);
for i:=1 to n do
readln(f,a[i]);
rewrite(f1);
if n = 1 then writeln(f1,' khong doi xung'){ quy uoc : day so co 1 chu so khong the doi xung }
else
for i:=1 to n do
if a[1] = a[n-1] then dem:=1 else dem:=2;
if dem=1 then writeln(f1,'doi xung');
if dem=2 then writeln(f1,'khong doi xung');
close(f);
close(f1);
end.