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 mod = sc.nextInt();
		long k = sc.nextInt();
		if ((left * k - 1) / mod < right * k / mod || k == 0 || left == 0) {
		    System.out.println("Yes");
		} else {
		    System.out.println("No");
		}
	}
}