#include <bits/stdc++.h>
using namespace std;
int main() {
  int N;
  cin >> N;
  vector<double> V(N);
  for (int i = 0; i < N; i++) cin >> V[i];
  double min = 100000007;
  int tmp;
  while (V.size() != 1) {
    min = 100000007;
    double ans;
    sort(V.begin(), V.end());
    for (int j = 0; j < V.size() - 1; j++) {
      if (min > V[j + 1] - V[j]) {
        min = V[j + 1] - V[j];
        ans = V[j + 1] + V[j];
        tmp = j;
      }
    }
    V.erase(V.begin() + tmp);
    V.erase(V.begin() + tmp);
    V.push_back(ans / 2.0);
  }
  cout << V[0] << endl;
}
