N = int(input())
A = [int(i) for i in input().split()]
B = [int(i) for i in input().split()]

cnt = 0
import itertools as it 
for i in it.permutations(range(N)):
    #print(i)
    for j in it.permutations(range(N)):
        s = 0
        for k in range(N):
            if A[i[k]]>B[j[k]]:
                s += 1
        if s>N//2: cnt += 1 
c = 1
for i in range(1, N+1):
    c *= i
c *= c
print(cnt/c)