Program wanted;
Uses crt;
Var t: boolean;
n,i: longint;
Begin
clrscr;
t := true;
write('nhap n=');
readln(n);
If n<=1 Then t := false;
For i:=2 To trunc(sqrt(n)) Do
If n Mod i=0 Then t := false;
If t=true Then writeln('n la so nguyen to')
Else writeln('n ko la so nguyen to');
readln
End.