import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        int A, B, C, D;
        Scanner sc = new Scanner(System.in);
        A = sc.nextInt();
        B = sc.nextInt();
        C = sc.nextInt();
        D = sc.nextInt();
        if(B >= C) System.out.println("Yes");
        else
        {
          int check = ((C/B+(C%B == 0 ? 0 : 1)) <= (A/D+(A%D == 0 ? 0 : 1))) ? 1 : 0;
          switch (check)
          {
              case 1:
                  System.out.println("Yes");
                  break;
              case 0:
                  System.out.println("No");
                  break;
          }

        }

    }
}

/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