#include <bits/stdc++.h>
using namespace std;
 
int main() {
    int a, b, c, d;

    cin >> a >> b >> c >> d;
while((a>0) && (b > 0)){
    a = a - d;
    c = c - b;
}
    if(c < 1){
        cout << "Yes" << endl;
        return 0;
    }else if(a < 1)){
        cout << "No" << endl;
    }
}
