#include <bits/stdc++.h>
using namespace std;
int main() {
  int A, flg = 0;
  double ans = 0.0, ans2;
  cin >> A;
  vector<int> num(A);
  for (int i = 0; i < A; i++) {
    cin >> num.at(i);
  }
  sort(num.begin(), num.end(), greater<int>());
  if (A < 3) {
    ans2 = (double)(num.at(0) + num.at(1)) / 2.0;
    cout << ans2 << endl;
    return 0;
  }
  for (int i = 2; i < A; i++) {
    if (flg == 0) {
      ans += (num.at(i - 1) + num.at(i)) / 2;
      flg = 1;
    } else {
      ans += (ans + num.at(i)) / 2;
    }
  }
  ans2 = (num.at(0) + ans) / 2;
  cout << ans2 << endl;
  return 0;
}
