from itertools import permutations

N = int(input())
A = [int(i) for i in input().split()]
B = [int(i) for i in input().split()]
aw = 0
tn = 0
for permA in permutations(A):
    for permB in permutations(B):
        tn += 1
        aw += sum(permA[i]>permB[i] for i in range(N)) > N//2
print(aw / tn)