#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int arr[n];
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
  }
  float b = (arr[0] + arr[1]) / 2.0;
  for (int i = 2; i < n; i++) {
    b = (b + arr[i]) / 2.0;
  }
  cout << (float)b;
  return 0;
}
