using System;

public class Hello
{
    public static void Main()
    {
        string[] line = Console.ReadLine().Trim().Split(' ');
        var n = int.Parse(line[0]);
        var m = int.Parse(line[1]);
        line = Console.ReadLine().Trim().Split(' ');
        var x = int.Parse(line[0]);
        var y = int.Parse(line[1]);
        var ans1 = getC(n, m, x);
        var ans2 = getC(n, m, y);
        Console.WriteLine(ans1 == ans2 ? "YES" : "NO");
    }
    public static int getC(int n, int m, int x)
    {
        var a = x % m;
        var b = (x + m - 1) / m;
        if (b % 2 == 1)
        {
            if (a == 0) return m;
            else return a;
        }
        else
        {
            if (a == 0) return 1;
            else return m + 1 - a;
        }
    }
}