#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n, t, k, d;
  cin >> n >> t >> k >> d;
  int cnt1 = 0, cnt2 = 0;
  int second = 0, i = 1;
  bool flag = false;
  while (second < n) {
    if (i > d) cnt2++;
    cnt1++;
    if (cnt1 == t) {
      second += k;
      cnt1 = 0;
    }
    if (cnt2 == t && second < n) {
      flag = true;
      break;
    }
    i++;
  }
  flag ? cout << "YES\n" : cout << "NO\n";
  return 0;
}
