#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int r;
  cin >> r;
  n--;
  while (n--) {
    int a;
    cin >> a;
    r = a + r / 2;
  }
  cout << fixed << setprecision(6) << r << "\n";
}
