uses crt;
var i,n,dem:integer;
begin
clrscr;
write('nhap so nguyen duong n ');readln(n);
dem:=0;
for i:=1 to n do if n mod i = 0 then dem:=dem+1;
if (n<2) or (dem< > 2) then writeln('n, khong phai la so nguyen to')
else if dem=2 then write(n,'la so nguyen to');
readln
end.