#include <bits/stdc++.h>
using namespace std;
int main() {
  int N;
  cin >> N;
  vector<double> v;
  for (int i = 0; i < N; i++) {
    double temp;
    cin >> temp;
    v.push_back(temp);
  }
  sort(v.begin(), v.end());
  double result;
  double kako = 0;
  for (int i = 0; i < N; i += 2) {
    if (kako == 0) {
      result = (v[i] + v[i + 1]) / 2;
    } else {
      result = (kako + v[i]) / 2;
    }
    kako = result;
  }
  cout << setprecision(10) << fixed << result;
  return 0;
}
