#include <bits/stdc++.h>
using namespace std;
int n, a[51];
double num;
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
  num = a[n];
  for (int i = n - 1; i > 0; i--) num = (num + a[i]) / 2.0;
  printf("%.5lf", num);
  return 0;
}
