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


class Program
{
    public void Proc()
    {
        Reader.IsDebug = false;
        long[] inpt = Reader.ReadLine().Split(' ').Select(a => long.Parse(a)).ToArray();
        long h = inpt[0];
        long w = inpt[1];
        long n = inpt[2];
        long k = inpt[3];

        if ((h + w - 1 - k) % n == 0)
        {
            Console.WriteLine("YES");
        }
        else
        {
            Console.WriteLine("NO");
        }
    }

    public class Reader
    {
        public static bool IsDebug = true;
        private static String PlainInput = @"


1 2 2 1



";
        private static System.IO.StringReader Sr = null;
        public static string ReadLine()
        {
            if (IsDebug)
            {
                if (Sr == null)
                {
                    Sr = new System.IO.StringReader(PlainInput.Trim());
                }
                return Sr.ReadLine();
            }
            else
            {
                return Console.ReadLine();
            }
        }
    }
    static void Main()
    {
        Program prg = new Program();
        prg.Proc();
    }
}