#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <stack>
#include <map>
using namespace std;

int main() {
    int n;
    while (scanf("%d", &n) != EOF) {
        if (n <= 0 || n == 1) {
            printf("no\n");
            continue;
        }
        int i;
        for (i = 2; i <= n / 2; i++) {
            if (n % i == 0) {
                printf("no\n");
                break;
            }
        }
        if (i > n / 2) {
            printf("yes\n");
        }
    }
    return 0;
}