program ct

uses crt;

var  k,i:integer;

begin

clrscr;

write('nhap k:=');readln(k);

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

begin

i:=2;

while k mod i<>0 do i:=i+1;

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

readln

end.

#include <bits/stdc++.h>
using namespace std;
int main(){
    int n;
    cin>>n;
    if(n < 2){
        cout<<"khong phai la so nguyen to";
        return 0;
    }
    int count = 0;
    for(int i = 2; i <= sqrt(n); i++){
        if(n % i == 0){
            count++;
        }
    }
    if(count == 0){
        cout<<"la so nguyen to";
    }else{
        cout<<"khong phai la so nguyen to";
    }
    //samon247
    return 0;
}