package No300台;

import java.util.Scanner;

public class Main{
	public static void main(String[] args) {
		solver();
	}

	static void solver() {
		Scanner sc = new Scanner(System.in);
		long n = sc.nextLong();
		long m = sc.nextLong();
		long x = sc.nextLong() - 1;
		long y = sc.nextLong() - 1;
		x = x % (2 * m);
		y = y % (2 * m);
		if (x == y) {
			System.out.println("YES");
		} else if (Math.abs(x + y) == 2 * m - 1) {
			System.out.println("YES");
		} else {
			System.out.println("NO");
		}
	}
}