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();

 		int counta = 0;
        while(C-B>0){
            C -= B;
                counta++;
        }
        int countt = 0;
        while(A-D>0){
            A -= D;
                countt++;
        }
        if(counta<=countt){
        System.out.println("Yes");
        }else{
        System.out.println("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