#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
  int N;
  cin >> N;
  vector<double> data(N);
  for (int i = 0; i < N; i++)
    ;
  { cin >> data.at(N); }
  sort(data.begin(), data.end());
  double answer = data.at(0);
  for (int i = 1; i < N + 1; i++) {
    answer = (answer + data.at(i)) / 2;
  }
  cout << answer << endl;
}
