from itertools import *

N = int(input())
A = list(map(int, input().split()))
B = list(map(int, input().split()))
ans = 0
for a in permutations(A):
    for b in permutations(B):
        cnt = 0
        for i in range(N):
            if a[i] > b[i]:
                cnt += 1
        if cnt * 2 > N:
            ans += 1

for i in range(1, N + 1):
    ans /= i * i
print(ans)