#include <bits/stdc++.h>
using namespace std;
int main() {
  long long N;
  cin >> N;
  vector<int> v(N);
  for (int i = 0; i < N; i++) cin >> v[i];
  priority_queue<int, vector<int>, greater<int>> PQ;
  for (int i = 0; i < N; i++) PQ.push(v[i]);
  double ans = 0;
  int cnt = 0;
  while (!PQ.empty()) {
    double t = PQ.top();
    PQ.pop();
    ans += t / pow(2, N - cnt - 1);
    if (cnt == N - 2) {
      ans += PQ.top() / 2;
      PQ.pop();
    }
    cnt++;
  }
  cout << fixed << setprecision(10) << ans << endl;
}
