#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n;
  cin >> n;
  vector<long long int> v;
  for (long long int i = 0; i < n; i++) {
    long long int k;
    cin >> k;
    v.push_back(k);
  }
  double ans = (v[0] + v[1]) / 2.0;
  for (long long int i = 2; i < n; i++) {
    ans = (ans + v[i]) / 2.0;
  }
  cout << ans << endl;
}
