import java.util.*;

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