#include <bits/stdc++.h>
using namespace std;
int main() {
  cin.tie(0);
  ios::sync_with_stdio(0);
  int n;
  cin >> n;
  vector<double> a(n);
  for (int i = 0; i < n; i++) cin >> a[i];
  double ans = 0;
  for (int i = 1; i < n; i++) {
    a[i] = (a[i - 1] + a[i]) / 2.0;
    ans = a[i];
  }
  printf("%.5lf", ans);
  return 0;
}
