#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
  int N;
  cin >> N;
  vector<double> v(N);
  for (int i = 0; i < N; i++) cin >> v.at(i);
  sort(v.begin(), v.end());
  int i = 0;
  while (i < N) {
    if (N - i == 2) {
      v.at(i + 1) = (v.at(i) + v.at(i + 1)) / 2;
      break;
    }
    if (N - i == 3) {
      v.at(i + 2) = (v.at(i) + v.at(i + 1) + 2 * v.at(i + 2)) / 4;
      break;
    }
    v.at(i + 1) = (v.at(i) + v.at(i + 1)) / 2;
    if (v.at(i + 3) < v.at(i + 1)) {
      ++i;
      continue;
    } else {
      v.at(i + 3) = (v.at(i + 2) + v.at(i + 3)) / 2;
      v.at(i + 2) = v.at(i + 1);
      i += 2;
      continue;
    }
  }
  cout << v.at(N - 1) << endl;
  return 0;
}
