from itertools import permutations

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

game, win = 0, 0

for X in permutations(B, N):
    game += 1
    cnt = 0
    for a, b in zip(A, X):
        if a > b:
            cnt += 1
    if 2*cnt > N:
        win += 1

print(win/game)