HW1_prime

#include <cstdio>

int main()
{
    int fl = 0, k = 0;
    scanf("%d", &k);
    for (int i = 2; i*i <= k); ++i){
        if (k % i == 0){
            fl = 1;
            printf("NO\n");
            break;
        }
    }
    if (fl == 0)
        printf("YES\n");
    return 0;
}