#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];
  }
  while (v.size() > 1) {
    sort(v.begin(), v.end());
    double diff = *v.end();
    int idx;
    double avg;
    for (int i = 0; i < v.size() - 1; i++) {
      if (v[i + 1] - v[i] < diff) {
        diff = v[i + 1] - v[i];
        idx = i;
        avg = v[i + 1] + v[i];
        avg /= 2.0;
      }
    }
    v.erase(v.begin() + idx, v.begin() + idx + 2);
    v.push_back(avg);
  }
  cout << v[0] << endl;
  return 0;
}
