import numpy as np


def get_answer(n, a):
    n = int(n)
    a = [int(v) for v in a.split(" ")]
    indexes_all = create_index(n)
    v_max = -1
    for indexes in indexes_all:
        v = a[indexes[0]]
        for i in range(1, len(indexes)):
            v = (v + a[indexes[i]]) / 2
        if v > v_max:
            v_max = v
    return v_max


def create_index(n):
    ret_all = []
    index_queue = np.arange(0, n)
    ret = []
    search_index(index_queue, ret_all, ret, n)
    return ret_all


def search_index(index_q, ret_all, ret, n):
    if n <= 0:
        ret_all.append(list(ret))
        return
    for i in range(n):
        index = index_q[i]
        index_q = np.delete(index_q, i)
        ret.append(index)
        search_index(index_q, ret_all, ret, n - 1)
        index_q = np.insert(index_q, i, index)
        ret.pop()


if __name__ == "__main__":
    input1 = input()
    input2 = input()
    print(get_answer(input1, input2))
