import itertools

n = int(input())
v = list(map(int, input().strip().split()))

ans_list = []

def calcurater(a_list):
  ans = (a_list[0] + a_list[1]) / 2
  for a in range(len(a_list) - 2):
    ans = (ans + a_list[a + 2]) / 2

  return ans

for i in itertools.permutations(v):
  ans_list.append(calcurater(list(i)))


print(max(ans_list))
