import java .util.Scanner;

public class Main{
    public static void main(String[] args){
	Scanner sc = new Scanner(System.in);
	int a = sc.nextInt();
	int b = sc.nextInt();
	int c = sc.nextInt();
	int d = sc.nextInt();

	while(true){
	    //高橋の攻撃
	    c -= b;
	    if(c<=0) break;
	    //高橋が攻撃される
	    a -= d;
	    if(a<=0) break;
	}
	if(c<=0) System.out.print("Yes");
	else if(a<=0) System.out.print("No");
    }
}

/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