#include <iostream>
using namespace std;

bool isPrime(int x){
	if(x < 2)return false;
	for(int i = 2;i*i <= x;i++){
		if(x%i==0)
			return false;
	}
	return true;
}

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