import java.util.*;

class Main2{
    public static void main(String[] args){
        // 入力受付
        Scanner sc = new Scanner(System.in);    //scanner
        int A = sc.nextInt();
        int B = sc.nextInt();
        int C = sc.nextInt();
        int D = sc.nextInt();

        // バトル
        while(true){
            // 高橋くんの攻撃
            C-=B;
            if(C<=0){
                System.out.println("Yes");
                break;
            }
            // 青木くんの攻撃
            A-=D;
            if(A<=0){
                System.out.println("No");
                break;
            }
        }
    }
}


// 別解
class Main{
    public static void main(String[] args){
        // 入力受付
        Scanner sc = new Scanner(System.in);    //scanner
        int A = sc.nextInt();
        int B = sc.nextInt();
        int C = sc.nextInt();
        int D = sc.nextInt();

        // 計算
        if( (A+D-1)/D >= (C+B-1)/B)
            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