#include <bits/stdc++.h>
using namespace std;
int main() {
  int N;
  cin >> N;
  vector<int> v(N);
  for (int i = 0; i < N; i++) {
    cin >> v.at(i);
  }
  double sum = 0.0;
  reverse(v.begin(), v.end());
  sum = (v.at(0) + v.at(1)) / 2;
  for (int i = 2; i < v.size(); i++) {
    sum = (sum + v.at(i)) / 2;
  }
  cout << sum << endl;
}
