#include <bits/stdc++.h>

using namespace std;

int main()
{
    int n;

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