#include <stdio.h>

#include <math.h>

int main()
{
    int n;
    while (scanf("%d", &n) != EOF)
    {
        int flag = 0;
        if (n <= 1)
        {
            flag = 1;
        }

        for (int i = 2; i <= sqrt(n); i++)
        {
            if (n % i == 0)
            {
                flag = 1;
                break;
            }
        }

        if (flag == 0)
        {
            printf("yes\n");
        }
        else
        {
            printf("no\n");
        }
    }

    return 0;
}