bai 3; xac dinh so doi xung

program bai3;
var s:string;
    i,l:integer;
    kt:boolean;
begin
writeln('nhap chuoi so bat ky');
readln(s);
kt:=(true);
l:=length(s);
for i:=1 to length(s) div 2 do
if s[i]<>s[l-i+1] then kt:= (false);
if kt then writeln('chuoi nay doi xung')
else writeln(' chuoi so nay khong doi xung');
readln;
end.