#include <bits/stdc++.h>
using namespace std;
int MOD = 1e9 + 7;
int INF = 1e9;
int n, k, t, d;
string s;
int solve() {
  cin >> n >> t >> k >> d;
  int batch = (n + k - 1) / k;
  int fst = batch * t;
  int now = 0;
  while (batch > 0) {
    now++;
    if (now % t == 0) batch--;
    if (now > d && now % t == d % t) batch--;
  }
  if (now < fst)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
  return 0;
}
int main() {
  ios::sync_with_stdio(0);
  solve();
  return 0;
}
