#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, t, k, d;
  cin >> n >> t >> k >> d;
  int prod = 0;
  int x = 0;
  int y = 0;
  int z = 0;
  while (n > prod) {
    x++;
    if (x % t == 0) {
      prod = prod + k;
    }
    if (x > d) {
      y++;
      if (y % t == 0) {
        prod = prod + k;
      }
    }
  }
  prod = 0;
  while (n > prod) {
    z++;
    if (z % t == 0) {
      prod = prod + k;
    }
  }
  if (x < z) {
    cout << "YES";
  } else {
    cout << "NO";
  }
  return 0;
}
