n = int(input())
*a, = map(int,input().split())
*b, = map(int,input().split())
from itertools import permutations
ans = 0
for pa in permutations(a):
    for pb in permutations(b):
        if sum(u > v for u,v in zip(pa,pb)) > n//2:
            ans += 1
print(ans/([0,1,2,6,24][n]**2))