uses crt;
var n:integer;
begin
clrscr;
write('Nhap so nguyen duong: ');readln(n);
while n<=0 do
begin
write('Nhap lai: ');
readln(n)
end;
If n mod 3 = 0 then writeln('Chia het cho 3');
If n mod 3 <>0 then writeln('Khong chia het cho 3');
readln;
end.