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

class Program
{
    public void Proc()
    {
        Reader.IsDebug = false;
        long[] inpt = Reader.ReadLine().Split(' ').Select(a=>long.Parse(a)).ToArray();

        long seitoCount = inpt[0];
        long classCount = inpt[1];

        inpt = Reader.ReadLine().Split(' ').Select(a=>long.Parse(a)).ToArray();
        long hanako = inpt[0] - 1;
        long taro = inpt[1] - 1;
        
        long hanaFrom = hanako - (hanako % (classCount * 2));

        long taroFrom = taro - (taro % (classCount * 2));

        long hanaClass = hanako % classCount;
        if(hanako >= hanaFrom + classCount) {
            hanaClass = classCount - 1 - hanaClass;
        }
        long taroClass = taro % classCount;
        if(taro >= taroFrom + classCount) {
            taroClass = classCount - 1 - taroClass;
        }
        string ans = "NO";
        if(hanaClass == taroClass) {
            ans = "YES";
        }
        Console.WriteLine(ans);
    }


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

10 2
4 5


 
";
        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();
    }
}