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

int n; 

bool cheak(int x)
{
	if(x <= 0 || x == 1) return false;
	
	for(int i = 2; i <= n / i; i ++)
		if(x % i == 0) return  false;
		
	return true;
} 

int main()
{
	while(cin >> n)
	{
		if(cheak(n)) cout << "yes" << endl;
		else cout << "no" << endl;
	}
    return 0;
}