#include <bits/stdc++.h>
using namespace std;

int main(){
    int a,b,c,d;
    cin >> a >> b >> c >> d;
    if(c/b > a/d){
        cout << "Yes" << endl;
    }else if(c/b < a/d){
        cout << "No" << endl;
    }else{
        if(a % d > 0){
            cout << "Yes" << endl;
        }else{
            cout << "No" << endl;
        }
    }
    return 0;
}