#yuki_133
import itertools

def game(x,y):
 cnt=0
 for i in xrange(len(x)):
  if x[i]>y[i]:
   cnt+=1
  else:
   cnt-=1
 return cnt

n=int(raw_input())
a=map(int,raw_input().split())
b=map(int,raw_input().split())
la=list(itertools.permutations(a))
lb=list(itertools.permutations(b))

cnt2=0
for i in la:
 for j in lb:
  if game(i,j)>0:
   cnt2+=1
  
print 1.0*cnt2/(len(la)*len(lb))