import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Set;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		final long N = sc.nextInt();
		final long M = sc.nextInt();
		final long X = sc.nextInt() - 1;
		final long Y = sc.nextInt() - 1;
		
		long X_mod2M = X % (2 * M);
		if(X_mod2M >= M){ X_mod2M = (M - 1) - (X_mod2M - M); }
		long Y_mod2M = Y % (2 * M);
		if(Y_mod2M >= M){ Y_mod2M = (M - 1) - (Y_mod2M - M); }
		
		System.out.println((X_mod2M== Y_mod2M) ? "YES" : "NO");
	}

}