import itertools

n = int(input())
food = [int(x) for x in input().split()]

food_p = list(itertools.permutations(food))

max_val = -1

if len(food) == 1:
    print(food[0])
elif len(food) == 2:
    print(sum(food) / 2)
else:
    for p in food_p:
        value = (p[0] + p[1]) / 2
        for val in p[2:]:
            value = (value + val) / 2

        if max_val < value:
            max_val = value

    print(max_val)