import itertools
_ = int(input())
u_list = [int(input()) for i in range(_)]
s_list = []
for s in itertools.permutations(u_list):
  s = list(s)
  _sum = (s.pop(0) + s.pop(0)) / 2
  while s:
    _sum = (_sum + s.pop(0)) / 2
  s_list.append(_sum)
print(max(s_list))