import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc=new Scanner(System.in);
		
		int a=sc.nextInt();		//たかはし体力
		int b=sc.nextInt();		//たかはし攻撃
		int c=sc.nextInt();		//あおき体力
		int d=sc.nextInt();		//あおき攻撃
		
		while(a>0&&c>0) {
			a=a-d;
			c=c-b;
		}
		if(c<=0) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		}
		sc.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