from itertools import permutations

n = int(input())
A = [int(x) for x in input().split()]
B = [int(x) for x in input().split()]

fac = 1
for i in range(1, n + 1):
    fac *= i

res = 0
for a in permutations(A):
    for b in permutations(B):
        wins = 0
        for i in range(n):
            if a[i] > b[i]:
                wins += 1
        if wins > n / 2:
            res += 1

ans = res / (fac**2)
print(ans)