import copy

limit = int(input())
vs = list(map(int,input().split()))
selected = []
maximum = 0

for x in vs:
    selected.append(False)

def fusion(x, y):
    # print("fusion {}, {}, {}".format(x, y, (x+y) / 2.0))
    return (x + y) / 2.0

def selection(elements, selected, limit):
    global maximum
    # print(elements)
    # print(selected)
    for xi, x in enumerate(elements):
        if selected[xi] == True:
            continue
        selected[xi] = True
        for yi, y in enumerate(elements):
            if selected[yi] == True:
                continue
            selected[yi] = True

            if len(elements) == 2:
                maximum = max(maximum, fusion(elements[xi], elements[yi]))
                return

            new_array = []
            new_selected = []
            for si, s in enumerate(selected):
                if s == False:
                    new_array.append(elements[si])
                    new_selected.append(False)
            new_selected.append(False)
            new_array.append(fusion(elements[xi], elements[yi]))
            # print("{} {}".format(elements[xi], elements[yi]))
            # # print("limit is {}".format(limit))
            selection(new_array, new_selected, limit)

            selected[yi] = False
        selected[xi] = False

selection(vs, selected, limit-1)

print (maximum)

