#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> vect(n);
  for (int i = 0; i < n; i++) cin >> vect[i];
  sort(vect.begin(), vect.end());
  float num = 0.00;
  num = vect[0] + vect[1];
  for (int i = 2; i < n; i++) {
    num = num + ((int)pow(2, i - 1)) * vect[i];
  }
  cout << (num / ((float)pow(2, n - 1)));
}
