#include <bits/stdc++.h>
using namespace std;
int main(void) {
  int n;
  double a;
  cin >> n;
  std::deque<double> deq;
  for (int i = 0; i < n; i++) {
    cin >> a;
    deq.emplace_back(a);
  }
  sort(deq.begin(), deq.end());
  double tmp = 0.0;
  for (int j = 0; j < n; j += 2) {
    if (j == 0) {
      tmp = (deq[j] + deq[j + 1]) / 2;
    } else {
      tmp = (tmp + deq[j]) / 2;
    }
  }
  cout << tmp << endl;
}
