#include <bits/stdc++.h>
using namespace std;
const int mxN = 1e5;
void solve() {
  int n, t, k, d;
  cin >> n >> t >> k >> d;
  int ans = 0;
  if (n <= k) {
    cout << "NO";
  } else if (t > d) {
    cout << "YES";
  } else if (t == d && n - k > k) {
    cout << "YES";
  } else {
    int temp = t;
    while (n > 0) {
      d--;
      temp--;
      if (temp == 0) {
        n -= k;
        temp = t;
        if (n <= 0) {
          cout << "NO";
          return;
        }
      }
      if (d == 0 && n > k) {
        cout << "YES";
        return;
      }
    }
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int T = 1;
  while (T--) {
    solve();
    cout << "\n";
  }
  return 0;
}
