#include <bits/stdc++.h>
using namespace std;
int main(int argc, char *argv[]) {
  int N;
  cin >> N;
  priority_queue<double> q;
  for (int i = 0; i < N; i++) {
    double cur;
    cin >> cur;
    q.push(cur);
  }
  cout << setprecision(15);
  if (N == 2) {
    double top = q.top();
    q.pop();
    double second = q.top();
    q.pop();
    cout << (top + second) / 2 << endl;
  } else {
    while (q.size() >= 3) {
      double top = q.top();
      q.pop();
      double second = q.top();
      q.pop();
      double third = q.top();
      q.pop();
      q.push(top);
      q.push((second + third) / 2);
    }
    {
      double top = q.top();
      q.pop();
      double second = q.top();
      q.pop();
      cout << (top + second) / 2 << endl;
    }
  }
  return 0;
}
