from itertools import permutations
n = int(input())
a = list(map(int,input().split()))
b = list(map(int,input().split()))
c = 0
for aa in permutations(a):
    for bb in permutations(b):
        aw = 0
        for i in range(n):
            aw += (aa[i] > bb[i])
        if aw > n / 2:
            c += 1
fac = [1] * (n + 1)
for i in range(n):
    fac[i + 1] = fac[i] * (i + 1)
print(c / (fac[n] ** 2))