a = int(input())
Lists = list(map(int, input().split()))

ma = []

for j in range(a):
    test = Lists.pop(0)
    for i in Lists:
        ma.append((i+test)/2)

ma2 = []
for j in ma:
    test = ma.pop(0)
    for i in ma:
        ma2.append((i+test)/2)

print (max(ma2))
