import itertools


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

C = list(itertools.permutations(V, N))

n = len(C)
ans = 0
for c in C:
    for v in range(n):
        a = C[v][0]
        for i in range(1, N):
            a = (a + C[v][i]) / 2
        ans = max(ans, a)
print(ans)