import copy
maximum = 0

def fusion(x, y):
    return (x + y) / 2.0

def selection(elements):
    global maximum

    if len(elements) == 2:
        maximum = max(maximum, fusion(elements[0], elements[1]))
        return

    for xi, x in enumerate(elements):
        for yi, y in enumerate(reverse(elements)):
            yi = len(elements) - yi - 1
            if xi == yi:
                continue
            new_array = []
            for ei, e in enumerate(elements):
                if ei != xi and ei != yi:
                    new_array.append(e)

            new_array.append(fusion(x, y))
            selection(new_array)

_ = int(input())
selection(list(map(int,input().split())))

print (maximum)

