#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, t, k, d, cakes_num = 0, i = 0;
  cin >> n >> t >> k >> d;
  bool flag = false;
  int without_second_oven = ceil(float(n) / k) * t;
  while (cakes_num < n) {
    i++;
    if (i % t == 0) {
      cakes_num += k;
    }
    if (flag && ((i - d) % t) == 0) {
      cakes_num += k;
    }
    if (i == d) {
      flag = true;
    }
  }
  string s = (without_second_oven <= i) ? "NO" : "YES";
  cout << s;
  return 0;
}
