using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;

class Program
{
    static void Main()
    {
        var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
        var s = Console.ReadLine();
        if (s != s.Trim())
        {
            Console.WriteLine("unexpected spase");
            return;
        }
        var a = s.Split().Select(int.Parse).ToArray();
        var t = Console.ReadLine();
        if (t != t.Trim())
        {
            Console.WriteLine("unexpected spase");
            return;
        }
        var b = t.Split().Select(int.Parse).ToArray();
        if (b[0] == b[1])
        {
            Console.WriteLine("unexpected input");
            return;
        }
        
        sw.WriteLine(cls(a[1], b[0]) == cls(a[1], b[1]) ? "YES" : "NO");
        sw.Flush();
    }
    static int cls(int m, int x)
    {
        int a = (x - 1) % (m * 2);
        return a < m ? a + 1 : m * 2 - a;
    }
}