#include <bits/stdc++.h>
using namespace std;
int main() {
  int j, n, i;
  double sum;
  cin >> n;
  double ara[i];
  for (i = 0; i < n; i++) cin >> ara[i];
  for (i = 0; i < n - 1; i++) {
    for (j = 0; j < n - 1; j++) {
      sum = (ara[j] + ara[j + 1]) / 2;
      ara[j + 1] = sum;
    }
  }
  cout << sum << endl;
  return 0;
}
