from itertools import permutations
from math import factorial
n=int(input())
a=list(map(int,input().split()))
b=list(map(int,input().split()))
deno=0
for per_a in permutations(range(n)):
    tmp_a=[]
    for i in range(n):
        tmp_a.append(a[per_a[i]])
    for per_b in permutations(range(n)):
        tmp_b=[]
        cnt=0
        for i in range(n):
            tmp_b.append(b[per_b[i]])
        for i in range(n):
            if tmp_a[i]>tmp_b[i]:
                cnt+=1
        if (n==1 and cnt==1) or (n==2 and cnt==2) or (n==3 and cnt>=2) or (n==4 and cnt>=3):
            deno+=1
print(deno/factorial(n)**2)