#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<double> vec(n);
  for (int i = 0; i < n; i++) {
    cin >> vec.at(i);
  }
  double min_1;
  double min_2;
  double avg;
  int index_1;
  int index_2;
  min_1 = vec.at(0);
  min_2 = vec.at(1);
  for (int k = 1; k = n - 1; k++) {
    for (int i = 0; i < n; i++) {
      if (vec.at(i) <= min_1) {
        min_1 = vec.at(i);
        index_1 = i;
      } else if (vec.at(i) <= min_2) {
        min_2 = vec.at(i);
        index_2 = i;
      }
    }
    avg = (min_1 + min_2) / 2;
    vec.at(index_1) = avg;
    vec.at(index_2) = 1001;
  }
  cout << avg << endl;
}
