#include <bits/stdc++.h>
using namespace std;
int N;
double ANS = 0;
void calc(vector<int>& nums, vector<int> vec) {
  double tmp = vec[nums[0]];
  for (int i = 0; i < N - 1; i++) {
    tmp = (tmp + vec[nums[i + 1]]) / 2;
  }
  ANS = max(ANS, tmp);
}
int main() {
  cin >> N;
  vector<int> vec;
  for (int i = 0; i < N; i++) {
    int v;
    cin >> v;
    vec.push_back(v);
  }
  vector<int> nums(N);
  iota(nums.begin(), nums.end(), 0);
  do {
    calc(nums, vec);
  } while (next_permutation(nums.begin(), nums.end()));
  cout << ANS << endl;
  ;
}
