import itertools
import math
n=int(input());
a=list(map(int,input().split()));
b=list(map(int,input().split()));
ans=0
for v in itertools.permutations(a,n):
    num=0
    for i in range(n):
        num+=(v[i]>b[i])
    if num*2>n:
        ans+=1
        
print(ans/math.factorial(n))