import java.util.*;

public class Main {
    public static void main (String[] args) {
        Scanner scanner = new Scanner(System.in);

        int A = scanner.nextInt();
        int B = scanner.nextInt();
        int C = scanner.nextInt();
        int D = scanner.nextInt();

        while (C > 0 && A > 0) {
            C -= B;
            if (C <= 0) {break;}
            A -= D;
        }

        String ans;
        if (C <= 0) {ans = "Yes";}
        else {ans = "No";}

        System.out.println(ans);

        scanner.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