#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, t, k, d;
  cin >> n >> t >> k >> d;
  int numberOfBaking = ceil(static_cast<float>(n) / k);
  int timeNeedByOne = numberOfBaking * t;
  int BakedDuringBuild = (t >= d ? 1 : ceil(static_cast<float>(d) / t));
  int timeNeedByTwo = ceil((numberOfBaking - BakedDuringBuild) / 2.0) * t + d;
  if (timeNeedByTwo < timeNeedByOne && numberOfBaking != BakedDuringBuild)
    cout << "YES";
  else
    cout << "NO";
  return 0;
}
