import java.util.*;
import java.io.*;

class Main {
	public static void main (String[] args) {
		Scanner input=new Scanner(System.in);
		int a,b,c,d;
		a=input.nextInt();
		b=input.nextInt();
		c=input.nextInt();
		d=input.nextInt();
		do{
		    c=c-b;
		  //   System.out.println("c" + c);
		    if(c<=0)
		        break;
		    a=a-d;
		  //  System.out.println("a" + a);
		    if(a<=0)
		        break;
		}while(c>0 && a>0);
		if(c<=0)
		     System.out.println("Yes");
		 else
		    System.out.println("No");
		input.close();
	}
}
/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