from itertools import permutations
n = int(input())
a = list(map(int, input().split()))
b = list(map(int, input().split()))
vs = 0
border = n//2
aaa = list(permutations(a, n))
bbb = list(permutations(b, n))
for aa in aaa:
    for bb in bbb:
        v = 0
        for x, y in zip(aa, bb):
            if x > y:
                v += 1
        if v > border:
            vs += 1
print(vs / (len(aaa) * len(bbb)))