import itertools

def factorial(n):
    if n<=1:
        return 1
    return n*factorial(n-1)

N=int(input())
a_card=[int(x) for x in input().split(" ")]
b_card=[int(x) for x in input().split(" ")]

a_win_pattern=0
for i in itertools.permutations(a_card):
    for j in itertools.permutations(b_card):
        a_win=0
        for k in range(N):
            if i[k]>j[k]:
                a_win+=1
        if a_win>N-a_win:
            a_win_pattern+=1

print(a_win_pattern/factorial(N)**2)