import java.util.*;

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