#include <bits/stdc++.h>
using namespace std;
using ll = long long;
template <class T>
bool chmax(T& prov, const T& cur) {
  if (cur > prov) {
    prov = cur;
    return true;
  }
  return false;
}
template <class T>
bool chmin(T& prov, const T& cur) {
  if (cur < prov) {
    prov = cur;
    return true;
  }
  return false;
}
int main() {
  int N;
  cin >> N;
  vector<double> v(N);
  for (int i = 0, i_len = (N); i < (int)N; i++) {
    cin >> v[i];
  }
  while (v.size() > 1) {
    double min_v = DBL_MAX;
    int index = 0;
    for (int i = 0, i_len = (v.size() - 1); i < (int)v.size() - 1; i++) {
      if (chmin(min_v, v[i] + v[i + 1])) {
        index = i;
      }
    }
    v[index] = min_v / 2.0;
    v.erase(v.begin() + index + 1);
  }
  printf("%.6lf\n", v[0]);
  return 0;
}
