import itertools
N =int(input())
pa=[int(x) for x in input().split()]
pb=[int(x) for x in input().split()]
nv,nt=0,0
for p in itertools.permutations(pa):
    n=0
    for i in range(N):
        if p[i]>pb[i]:  n +=1
    if n*2>N:           nv+=1
    nt+=1
print(nv/nt)