import itertools
n=input()
a=map(int,raw_input().split())
b=map(int,raw_input().split())
w=0.
a=list(itertools.permutations(a))
b=list(itertools.permutations(b))
for i in a:
	for j in b:
		x=0
		for k in range(n):
			if i[k]>j[k]:
				x+=1
			else:
				x-=1
		if x>0:
			w+=1
print w/(len(a)*len(b))