def abc138_c():
    N = int(input())
    values = sorted(list(map(int, input().split())), reverse=True)

    ans = (values[0] + values[1]) / 2

    for v in range(2, N , 2):
        ans = (ans + values[v]) / 2

    print(ans)

if __name__ == '__main__':
    abc138_c()