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