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

int main() {
    int a,b,c,d;
    cin >> a >> b >> c >> d;
    while(1){
        c=c-b;
        if(c<=0){
            cout << "Yes" << endl;
            break;
        }
        a=a-d;
        if(a<=0){
            cout << "No" << endl;
            break;
        }
    }
}