def resolve():
    n = int(input())
    v = sorted(list(map(int, input().split())))
    while len(v) > 2:
        new_v = []
        for j in range(len(v) // 2)[::2]:
            new_v.append(sum(v[j:j + 2]) / 2)
        if len(v) % 2 == 1:
            new_v.append(v[-1])
        v = new_v
    print(sum(v) / 2)


if __name__ == "__main__":
    resolve()
