n=int(input())
a=list(map(int,input().split()))
b=list(map(int,input().split()))

def kaijo(k):
    ans=1
    for i in range(k,1,-1):
        ans*=i
    return ans

from itertools import permutations

a=list(permutations(a))
b=list(permutations(b))

cnt=0

for x in a:
    for y in b:
        if len([None for i in range(n) if x[i]>y[i]])>n/2:
            cnt+=1
print(cnt/kaijo(n)/kaijo(n))