uses crt;
var n,i:integer;k:boolean;
begin
clrscr;k:=true;
write('Nhap n:');readln(n);
if n<=1 then k:=false;
if n>=2 then
for i:=2 to n div 2 do
if n mod i=0 then k:=false;
if k=false then write(n,' khong la so nguyen to') else write(n,' la so nguyen to');
readln
end.