import java.util.*;
 
public class Main {
    public static void main(String[] args){
        Scanner scn = new Scanner(System.in);
        int A = scn.nextInt();
        int B = scn.nextInt();
        int C = scn.nextInt();
        int D = scn.nextInt();
        
        while(C>0 && A>0){
            C = C-B;
            
            if(C<=0){
                break;
            }
            
            A = A-D;
        }    
          
        if(C<=0){
                System.out.println("Yes");
            }
        else if(A<=0){    
               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