#include <bits/stdc++.h>
using namespace std;
int n;
float arr[100000];
float maxs = 0;
void permu(float a[], int k, int m) {
  int i, j;
  if (k == m) {
    float maxs2 = arr[0];
    for (int i = 1; i < n; i++) {
      maxs2 = (maxs2 + arr[i]) / 2;
    }
    if (maxs < maxs2) {
      maxs = maxs2;
    }
  }
  for (j = k; j <= m; j++) {
    swap(a[j], a[k]);
    permu(a, k + 1, m);
    swap(a[j], a[k]);
  }
}
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    scanf("%f", &arr[i]);
  }
  permu(arr, 0, n - 1);
  printf("%f", maxs);
  return 0;
}
