#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
using ll = long long;
using P = pair<int, int>;

int a, b, c, d;

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