# -*- coding: utf-8 -*-
from decimal import Decimal
from itertools import permutations

# 整数の入力
N = int(input())

# スペース区切りの整数の入力
V = list(map(Decimal, input().split()))

result = 0

for values in permutations(V, N):
    new_result = values[0]

    for value in values[1:]:
        new_result = (new_result + value) / 2

    if result < new_result:
        result = new_result

# 出力
print(result)
