#include <bits/stdc++.h>

#define REP(i, n) for (int i = 0; i < n; i++)
#define REPR(i, n) for (int i = n; i >= 0; i--)
#define FOR(i, m, n) for (int i = m; i < n; i++)
#define FORR(i, m, n) for (int i = m; i >= n; i--)
#define ALL(x) (x).begin(), (x).end()

using namespace std;
typedef long long ll;
typedef pair<ll, ll> P;
const ll INF = 1e15;

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