from itertools import permutations

N = int(input())
A = list(map(int, input().split()))
B = list(map(int, input().split()))
ans = 0
s = 0

for p in permutations(A):
    win, lose = 0, 0
    
    for i in range(N):
        if p[i]>B[i]:
            win += 1
        else:
            lose += 1
    
    if win>lose:
        ans += 1

    s += 1
    
print("{:.10f}".format(ans/s))