#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,cnt=0;
    cin>>n;
    for(int i=2;i<=sqrt(n);i++){
        
        if(n%i==0){
            cnt+=1;
            break;
        }
    }
    if(cnt==0){
        cout<<"yes";
    }
    else if(cnt>0||n==1){
        cout<<"no";
    }
    return 0;
}
/**************************************************************
	Problem: 1061
	User: luyanchen
	Language: C++
	Result: Wrong Answer
****************************************************************/