import itertools


N = int(input())
V = list(map(int, input().split()))

C = list(itertools.permutations(V, N))
S = set(C)
ans = 0
for s in S:
    a = s[0]
    for i in range(1, N):
        a = (a + s[i]) / 2
    ans = max(ans, a)
print(ans)