from itertools import permutations
N=int(input())
A=list(map(int,input().split()))
B=list(map(int,input().split()))
cnt=0
for perm in permutations(range(N)):
  res=0
  for i in range(N):
    if A[perm[i]]>B[i]:
      res+=1
    else:
      res-=1
  if res>0:
    cnt+=1
fac=1
for i in range(1,N+1):
  fac*=i
print(cnt/fac)