https://codeforces.com/group/n3sTiYtHxI/contest/348733/problem/B

#include <iostream>
#include<bits/stdc++.h>
#define ll long long
#define ull unsigned long long
using namespace std;

bool is_prime (ull n){
    if (n<2 || (n%2 == 0 && n != 2 ))   return false ;
    for(int i= 3  ; i<sqrt(n) ; i+=2){
        if (n % i == 0)   return false;

    }
    return true;
}

int main() {
   ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
 ull n ;
 cin>>n;

 if (is_prime(n))      cout<<"YES";
 else                  cout<<"NO";



    return 0;
}