using System;

public class Program

{

    public static void Main()

    {

    int num,count = 0;

    num = int.Parse(Console.ReadLine());

    for (int i=1;i<=num;i++)

        if (num%i==0)

            count++;

    if (count == 2)

        Console.WriteLine("YES");

    else if (count > 2)

        Console.WriteLine("NO");

    }

}