#include <bits/stdc++.h>
using namespace std;
#define SORT(a) sort((a).begin(), (a).end())
#define RSORT(a) reverse((a).begin(), (a).end())
#define rep(i, n) for (int i = 0; i < n; i++)
typedef long long ll;
const long long INF = 1LL << 60;
// const int INF=1010101010;
using Graph = vector<vector<int>>;

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