using System;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;
using static System.Math;

namespace SortItems
{
    class Program
    {
        static void Main(string[] args)
        {
            var num = Console.ReadLine().Split().Select(int.Parse).ToArray();
            var h = num[0];
            var w = num[1];
            var n = num[2];
            var k = num[3];

            var sum = (h + w) - 1;

            Console.WriteLine((sum % n) == k ? "YES" : "NO");


        }
    }
}