from itertools import permutations

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

game = 0
win = 0

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

p = win / game
print(p)