import sys
import itertools

N = int(input())

A= list(map(int,input().split()))


if N == 2:
    print((A[0] + A[1]) / 2)
    sys.exit()

list = []

for i in itertools.permutations(A):
    list.append(i)


countList = []

for i in list:
    count = 0
    for k in range(len(i) - 1):
        if count == 0:
            count = (i[k] + i[k + 1]) / 2
        else:
            count = (count + i[k + 1]) / 2
            countList.append(count)

print(max(set(countList)))