#include <bits/stdc++.h>
using namespace std;

bool issu(int n){
	for(int i=sqrt(n); i>1; i--){
		if(n%i==0) return false;
	}
	return true;
}
int main()
{
	int n;
	while(cin>>n){
		if(issu) cout<<"yes"<<endl;
		else cout<<"no"<<endl;
	}
}