n = int(eval(input()))

a = [int(i) for i in input().split()]

print((1 / sum(1 / ai for ai in a)))
n = int(eval(input()))

a = list(map(int, input().split()))

print((1 / sum(1 / ai for ai in a)))
n = int(eval(input()))
a = [int(i) for i in input().split()]
print((1 / sum(1 / ai for ai in a)))

n = int(eval(input()))
a = list(map(int, input().split()))
print((1 / sum(1 / ai for ai in a)))

-a = [int(i) for i in input().split()] +a = list(map(int, input().split()))