#include <bits/stdc++.h>
#pragma GCC optimize("O3")
using namespace std;
const int N = 1e3 + 5, M = 1e5 + 5;
long double a[N];
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  ;
  int n;
  cin >> n;
  for (int i = 0; i < n; ++i) cin >> a[i];
  for (int i = n - 2; ~i; --i) a[i] = (a[i] + a[i + 1]) / 2.0L;
  cout << fixed << setprecision(12) << a[0] << endl;
}
