import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] first = br.readLine().split(" ", 2);
        int n = Integer.parseInt(first[0]);
        int m = Integer.parseInt(first[1]);
        String[] second = br.readLine().split(" ", 2);
        int x = Integer.parseInt(second[0]);
        int y = Integer.parseInt(second[1]);
        if (getClass(x, m) == getClass(y, m)) {
            System.out.println("YES");
        } else {
            System.out.println("NO");
        }
    }
    
    static int getClass(int x, int m) {
        if ((x - 1) / m % 2 == 0) {
            if (x % m == 0) {
                return m;
            } else {
                return x % m;
            }
        } else {
            return m - (x - 1) % m;
        }
    }
}