#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> v(n, 0);
  for (int i = 0; i < n; i++) {
    cin >> v.at(i);
  }
  double result = 0;
  for (int i = n - 1; i > 0; i--) {
    sort(v.rbegin(), v.rend());
    result = v.at(i) + v.at(i - 1);
    result /= 2.0;
    v.pop_back();
    v.pop_back();
    v.push_back(result);
  }
  cout << setprecision(6) << result << endl;
}
