import itertools

N=int(input())
A=list(map(int,input().split()))
B=list(map(int,input().split()))
ans=0
for AA in itertools.permutations(A):
    if sum(a>b for a,b in zip(AA,B))*2>N:
        ans+=1
for i in range(1,N+1):
    ans/=i
print(ans)