#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  double v, x = 0.00;
  cin >> n >> v;
  for (int i = 0; i < n - 1; i++) {
    cin >> x;
    v = (v + x) / 2;
  }
  cout << v << endl;
}
