from itertools import permutations

n = int(input())
A = list(map(int, input().split()))
B = list(map(int, input().split()))
As = list(permutations(A, n))
Bs = list(permutations(B, n))

vic = 0
thr = n//2

for a in As:
    for b in Bs:
        tmp = len([i for i, j in zip(a, b) if i > j])
        if tmp > thr:
            vic += 1

print(vic / (len(As)*len(Bs)))