var s,s1,s2:string;
begin
write('nhap xau s: '); readln(s);
if (length(s) mod 2)<>0 then write('xau s khong phai la xau doi xung')
else
begin
s1:=copy(s,1,length(s) div 2);
s2:=copy(s,(length(s) div 2)+1, length(s) div 2);
if s1=s2 then write('xau s la xau doi xung')
else write('xau s khong phai la xau doi xung');
end;
readln;
readln;
end.