from itertools import permutations

N = int(input())
A = tuple(map(int, input().split()))
B = tuple(map(int, input().split()))

judge = N // 2
cnt1 = 0
cnt2 = 0

for cards_A in permutations(A):
    for cards_B in permutations(B):
        cnt1 += 1
        point = 0
        for ca, cb in zip(cards_A, cards_B):
            if ca > cb:
                point += 1
        if point > judge:
            cnt2 += 1

print(cnt2 / cnt1)