#include <bits/stdc++.h>
#define rep(i, a, n) for (int i = a; i < n; i++)
#define repr(i, a, n) for (int i = n - 1; i >= a; i--)
using namespace std;
using ll = long long;
using P = pair<int, int>;
template <typename T> void chmin(T &a, T b) { a = min(a, b); }
template <typename T> void chmax(T &a, T b) { a = max(a, b); }

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);

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