import sys
from math import ceil, floor, sqrt, sin, cos, pi
from itertools import accumulate, permutations, combinations
from fractions import gcd # 最大公約数
from collections import deque, Counter
from operator import itemgetter
from heapq import heappop,heappush
sys.setrecursionlimit(10**7)
def lcm(x, y): return ((x * y) // gcd(x, y)) # 最小公倍数
# list(map(int, input().split()))
n = int(input())
v = list(map(float, input().split()))

ans = []
for x in permutations(v):
    p = x[0]
    for i in range(1, n):
        p = (p + x[i])/2.0
    ans.append(p)
print(max(ans))