#include <bits/stdc++.h>
using namespace std;
void test_data(int N, vector<double> v) {
  N = 2;
  v = {3, 4};
  cout << v[0] << endl;
}
int input_data(int N, vector<double> v) {
  cin >> N;
  for (int i = 0; i < N; i++) {
    int x;
    cin >> x;
    v.push_back(x);
  };
}
double nabe(double x, double y) {
  double ans = (x + y) / 2;
  return ans;
}
int main() {
  int N = 3;
  vector<double> v = {500, 300, 200};
  cin >> N;
  for (int i = 0; i < N; i++) {
    int x;
    cin >> x;
  };
  for (int i = 0; i < v.size(); i++) {
  }
  sort(v.begin(), v.end());
  for (int i = 0; i < v.size(); i++) {
  }
  double x = nabe(v.at(0), v.at(1));
  for (int i = 2; i < v.size(); i++) {
    x = nabe(v.at(i), x);
  }
  cout << x << endl;
}
