#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int a[n];
  for (int i = 0; i < n; i++) cin >> a[i];
  double s = a[n - 1];
  for (int i = 1; i < n; i++) s = (a[n - i - 1] + s) / 2;
  cout << s;
}
