import java.util.*;
public class Main {
	public static void main(String[] args)  {
		Scanner scan = new Scanner(System.in);
		int a = Integer.parseInt(scan.next());
		int b = Integer.parseInt(scan.next());
		int c = Integer.parseInt(scan.next());
		int d = Integer.parseInt(scan.next());

		while(true){
			c -=b;
			if(c <= 0){
				System.out.println("Yes");
				break;
			}

			a -=d;
			if(a <= 0){
				System.out.print("No");
				break;
			}
		}

	}

}
//end
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz