#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> v(n);
  vector<double> d(n);
  for (int i = 0; i < (int)(n); i++) cin >> v[i];
  for (int i = 0; i < (int)(n - 1); i++) {
    sort(v.begin(), v.end());
    d[i] = (v[0] + v[1]) / 2;
  }
  cout << d[n - 2] << endl;
}
