import itertools

_ = int(input())
u_list = list(map(int, input().split()))
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))