from collections import deque
import itertools

N = int(input())
V = list(map(int, input().split()))
l = map(list, itertools.permutations(V))
r = list()
for lo in l:
    i = 0
    while (i + 1< len(lo)):
        if ((lo[i] + lo[i + 1]) / 2) not in lo:
            lo.append((lo[i] + lo[i + 1]) / 2)
        i+=2
    r.append(lo[-1])

print(max(r))