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

int main() {
  int a, b, c, d;
  int ta, ao, ta2, ao2;
  cin >> a >> b >> c >> d;
  if(a / d + a % d < c / b + c % b) cout << "No" << endl;
  else if(a / d + a % d >= c / b + c % b) cout << "Yes" << endl;
}