#include <bits/stdc++.h>
using namespace std;
int n;
vector<int> v(1005, 0);
void input() {
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> v.at(i);
  }
}
void solve() {
  vector<vector<double>> memo(n, vector<double>(n, 0.0));
  vector<int> select_order(n, 0);
  iota(select_order.begin(), select_order.end(), 1);
  deque<double> s;
  double max_val = 0.0;
  double a, b, c;
  do {
    s.clear();
    for (int i = 0; i < n; i++) {
      s.push_back(v.at(select_order.at(i) - 1));
    }
    while (s.size() != 1) {
      a = s.back();
      s.pop_back();
      b = s.back();
      s.pop_back();
      c = ((a + b) / 2.0);
      s.push_back(c);
    }
    if (c > max_val) {
      max_val = c;
    }
  } while (next_permutation(select_order.begin(), select_order.end()));
  cout << max_val << endl;
}
int main() {
  input();
  solve();
}
