import itertools

N = int(input())
v = list(map(int,input().split()))
ret = 0

numbers = list(itertools.permutations(v))

for _ in range(N):
  shadow = list(numbers[_])
#  print(shadow)
  for i in range(N-1):
    a = shadow.pop()
    b = shadow.pop()
    shadow.append((a+b)/2)
  ret = max(ret,shadow[0])

print(ret)
