#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> v(n);
  for (int i = 0; i < n; i++) cin >> v[i];
  double tmp = 0;
  double ans = 1001;
  for (int i = 0; i < n - 1; i++) {
    for (int j = i + 1; j < n; j++) {
      tmp = (v[i] + v[j]) / 2.0;
      if (tmp < ans) {
        ans = tmp;
      }
    }
  }
  sort(v.rbegin(), v.rend());
  for (int i = 0; i < n - 2; i++) {
    ans = (ans + v[i]) / 2.0;
  }
  cout << ans;
}
