#include<cmath>
#include<iostream>
using namespace std;

bool sushu(int n)
{
	if (n < 2)
	{
		return false;
	}
	else
	{
		for (int i = 2; i <= sqrt(n); i++)
		{
			if (n % i == 0)
				return false;
		}
	}
	return true;
}

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