import copy
maximum = 0

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

def selection(elements):
    global maximum

    if len(list(set(elements))) == 1:
        return elements[0]

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

    for xi, x in enumerate(elements):
        for yi, y in enumerate(elements):
            yi_ = len(elements) - 1 - yi
            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, elements[yi_]))
            selection(new_array)
            if xi > yi_:
                return


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

print (maximum)

