# coding: UTF-8
import sys
#sys.setrecursionlimit(n)
import heapq
import re
import bisect
import random
import math
import itertools
from collections import defaultdict, deque
from copy import deepcopy
from decimal import *

readl= lambda: list(map(int, sys.stdin.readline().split()))
readt= lambda: tuple(map(int, sys.stdin.readline().split()))
read = lambda: sys.stdin.readline().rstrip()
readi = lambda: int(read())
readmi = lambda: map(int, sys.stdin.readline().split())
readms = lambda: map(str, sys.stdin.readline().split())

n = readi()
l = readl()
mx = 0
def func(i, ll, s, size):
    global mx
    if size == 0:
        mx = max(mx, ll[0])
        return mx
    t = list(ll)
    base = t[i]
    t.pop(i)
    for j in range(size):
        p = t[0]
        p2 = (base + t[0]) / 2
        t.pop(0)
        t.append(p2)
        func(j, list(t), p2, size - 1)
        t.pop(-1)
        t.append(p)
for i in range(n):
    func(i, list(l), 0, n - 1)
print(mx)