import java.util.*;

public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		int left = sc.nextInt();
		int right = sc.nextInt();
		int m = sc.nextInt();
		long k = sc.nextInt();
		long leftCount = (left * k - 1) / m;
		long rightCount = right * k / m;
		if (leftCount == rightCount && k != 0) {
		    System.out.println("No");
		} else {
		    System.out.println("Yes");
		}
	}
}