#include <bits/stdc++.h>
using namespace std;
int main(void) {
  int n;
  int box[51];
  int x, y;
  int i, j, k;
  double a, b, MAX;
  cin >> n;
  for (i = 1; i <= n; i++) cin >> box[i];
  for (i = 1; i <= n - 1; i++) {
    for (j = i + 1; j <= n; j++) {
      x = box[i];
      y = box[j];
      a = (double)(x + y) / 2;
      for (k = 1; k <= n; k++) {
        if (k != i && k != j) {
          b = (double)(a + box[k]) / 2;
          a = b;
        }
      }
      MAX = max(MAX, a);
    }
  }
  printf("%.5lf\n", MAX);
  return 0;
}
