#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll MOD = 1000000007;
const double PI = 3.14159265358979;
const ll INF = pow(10, 18);
string abc = "abcdefghijklmnopqrstuvwxyz";
string ABC = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
int main() {
  ll n;
  cin >> n;
  vector<ll> a(n);
  for (ll i = 0; i < n; i++) {
    cin >> a[i];
  }
  sort(a.begin(), a.end());
  vector<ll> b(n - 1);
  b[0] = (a[0] + a[1]) / 2;
  for (ll i = 1; i < n - 1; i++) {
    b[i] = (b[i - 1] + a[i + 1]) / 2;
  }
  double k = b[n - 2];
  cout << fixed << setprecision(5);
  cout << k << endl;
}
