using System;

class A {
    static int N, M, X, Y;
    static void Main() {
        string[] A = Console.ReadLine().Split(' ');
        N = int.Parse(A[0]);
        M = int.Parse(A[1]);
        A = Console.ReadLine().Split(' ');
        X = int.Parse(A[0])-1;
        Y = int.Parse(A[1])-1;
        int Q, W;
        Q = (X / M) % 2 == 0 ? X % M : M - (X % M)-1;
        W = (Y / M) % 2 == 0 ? Y % M : M - (Y % M)-1;
        if (Q == W) {
            Console.WriteLine("YES");

        }
        else {
            Console.WriteLine("NO");

        }
    }
}