import java.util.Scanner;
//import java.util.Arrays;
public class Main{
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int tHp = sc.nextInt();
		int tAttack = sc.nextInt();
		int aHp = sc.nextInt();
		int aAttack = sc.nextInt();
		String result = "";
		while(true){
			aHp -= tAttack;
			if(aHp <= 0){
				result = "Yes";
				break;
			}
			tHp -= aAttack;
			if(tHp <= 0){
				result = "No";
				break;
			}
		}
		System.out.println(result);
	}
}

/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