#include <bits/stdc++.h>
using namespace std;
int main() {
  int n = 0;
  cin >> n;
  double* p = new double[n];
  for (int i = 0; i < n; i++) {
    cin >> p[0];
    if (i > 0) {
      p[i] += (p[i - 1] + p[i]) / 2;
    }
  }
  cout << p[n] << endl;
  delete p;
  return 0;
}
