#include <bits/stdc++.h>
using namespace std;
int main() {
  int N;
  cin >> N;
  double v[1000], v2;
  for (int i = 0; i < N; i++) {
    cin >> v[i];
  }
  for (int i = 1; i < N; i++) {
    v[i] = (v[i] + v[i - 1]) / 2;
  }
  cout << v[N - 1];
}
