#include <bits/stdc++.h>
using namespace std;
int main() {
  int N;
  cin >> N;
  vector<int> v(N);
  for (int i = 0; i < N; i++) cin >> v[i];
  sort(v.begin(), v.end(), greater<int>());
  double sum = 0;
  int a = 2;
  for (int i = 0; i < N - 1; i++) {
    sum += (double)v[i] / a;
    if (i == N - 2) sum += (double)v[N - 1] / a;
    a *= 2;
  }
  cout << fixed << setprecision(6) << sum << endl;
}
