#include <bits/stdc++.h>
using namespace std;
double s;
int main() {
  int n;
  cin >> n;
  vector<double> v(n);
  for (int i = 0; i < (int)(n); i++) cin >> v[i];
  sort(v.begin(), v.end());
  if (n == 2) {
    cout << (v[0] + v[1]) / 2.0 << endl;
    return 0;
  } else {
    for (int i = 0; i < (int)(n - 2); i++) {
      s = (((v[i] + v[i + 1]) / 2.0) + v[i + 2]) / 2.0;
    }
  }
  cout << s << endl;
}
