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


public class Main_yukicoder384 {

    public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
    	Printer pr = new Printer(System.out);

    	int h = sc.nextInt();
    	int w = sc.nextInt();
    	long n = sc.nextLong();
    	long k = sc.nextLong();

    	if ((h - 1 + w - 1) % n == k - 1) {
    		pr.println("YES");
    	} else {
    		pr.println("NO");
    	}

        pr.close();
        sc.close();
    }

	private static class Printer extends PrintWriter {
		Printer(PrintStream out) {
			super(out);
		}
	}
}