#include <bits/stdc++.h>
const int mxn = 1e5 * 4 + 10, mod = 1e9 + 7;
using namespace std;
long long phi(long long n);
long long gcd(long long a, long long b);
long long lcm(long long a, long long b);
long long n, m, t = 0, l, k, a, tmp, d;
int mn = 1e9, mx = -1;
int main() {
  cin >> n >> t >> k >> d;
  long long ao, bo, c, g;
  c = (n + k - 1) / k;
  ao = c * t;
  c -= d / t;
  g = d / t * t;
  c -= (d - g) / t;
  g += (d - g) / t * t;
  if (c % 2) {
    g += (c / 2 + 1) * t;
    d += (c / 2) * t;
  } else {
    g += (c / 2) * t;
    d += (c / 2) * t;
  }
  bo = max(d, g);
  cout << ((ao > bo) ? "YES" : "NO");
}
long long phi(long long n) {
  long long res = n, i = 2;
  for (; i * i <= n; i++)
    if (n % i == 0) {
      while (n % i == 0) n = n / i;
      res -= res / i;
    }
  if (n > 1) res -= res / n;
  return res;
}
long long gcd(long long a, long long b) { return (b == 0) ? a : gcd(b, a % b); }
long long lcm(long long a, long long b) { return a * b / gcd(a, b); }
