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();
		long y = sc.nextLong();
		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");
		}
	}
}