import java.util.*;

public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		int h = sc.nextInt();
		int w = sc.nextInt();
		int n = sc.nextInt();
		int k = sc.nextInt();
		int mod = (h + w - 1) % n;
		if (mod == k) {
		    System.out.println("YES");
		} else {
		    System.out.println("NO");
		}
	}
}