#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];
  }
  double a;
  a = (double)(v[0] + v[1]) / 2;
  for (int i = 2; i < n; i++) {
    a = (double)(a + v[i]) / 2;
  }
  cout << a;
}
