#include <bits/stdc++.h>
using namespace std;
int main() {
  int N;
  cin >> N;
  double v[N];
  for (int i = 0; i < N; i++) {
    cin >> v[i];
  }
  sort(v, v + N);
  double tmp = (v[0] + v[1]) / 2.0;
  double sum = 0.0;
  for (int i = 3; i < N; i++) {
    sum = (tmp + v[i]) / 2.0;
  }
  cout << sum << endl;
  return 0;
}
