#include <iostream>
#include <string>
#include <stack>
using namespace std;

int main(){
    int x;
    scanf("%d",&x);
    if(x<=1){printf("no\n");return 0;}
    for(int i=2;i<=x/2;i++){
        if(x%i==0){
            printf("no\n");
            return 0;
        }
    }
    printf("yes\n");
    return 0;
}