import java.util.Scanner;

public class Test {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt(), m = sc.nextInt(), x = sc.nextInt() - 1, y = sc.nextInt() - 1;
		int a, b;
		if ((x / m) % 2 == 0) {
			a = x % m;
		} else {
			a = m - 1 - (x % m);
		}
		if ((y / m) % 2 == 0) {
			b = y % m;
		} else {
			b = m - 1 - (y % m);
		}
		if (a == b) {
			System.out.println("YES");
		} else {
			System.out.println("NO");
		}
	}
}