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

int main () {
    double A, B, C, D;
    cin >> A >> B >> C >> D;
    if(ceil(C / B) <= ceil(A / D))
    {
        cout << "Yes" << endl;
    }
    else
    {
        cout << "No" << endl;
    }
}
