using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace YukiCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var va = Console.ReadLine().Split().Select(long.Parse).ToArray();
            Console.WriteLine((va[0] * va[1] + va[2] - 1) % va[2] + 1 == va[3] ? "YES" : "NO");
            Console.ReadLine();
        }
    }
}