import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] str = br.readLine().split(" ");
        String result = "Yes";

        int a = Integer.parseInt(str[0]);
        int b = Integer.parseInt(str[1]);
        int c = Integer.parseInt(str[2]);
        int d = Integer.parseInt(str[3]);

        while (a > 0 && c > 0) {
            c -= b;
            a -= d;
        }
        if (c > 0) {
            result = "No";
        }

        System.out.println(result);
    }
}

/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