program ct;

uses crt;

var n,i:integer;

begin

clrscr;

  write('nhap 1 so nguyen:=');readln(n);

     if n<=1 then writeln(n khong phai so nguyen to') else

begin

  i:=2;

    while n mod i<>0 do i:=i+1;

       if i=n then writeln(n,' la so nguyen to') else writeln(n,' khong la so nguyen to');

end;

readln

end.

Program FNG;
Uses crt;
Var n: qword;

Function ngto(a: qword): boolean;
Var i: longint;
Begin
        If a<2 then exit(false);
        For i:=2 to a div 2 do
                If a mod i = 0 then exit(false);
        exit(true);
End;

Begin
        Clrscr;
        Write('Nhap n: '); Readln(n);
        If ngto(n) then Write('YES')
        Else Write('NO');
        Readln
End.