#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<double> v(n);
  for (int i = 0; i < n; ++i) cin >> v.at(i);
  for (int i = 0; i < n - 1; ++i) {
    v.at(i + 1) = (v.at(i) + v.at(i + 1)) / 2.0;
  }
  cout << v.at(n - 1) << endl;
  return 0;
}
