import itertools
N = int(input())

a = list(map(int, input().split()))
b = list(map(int, input().split()))

per = itertools.permutations(list(range(N)), 2)

cnt = 0
count = 0
for (x, y) in per:
    if a[x]>b[y]:
        cnt += 1
    count += 1

if count ==0:
    print(0)

else:
    ans = cnt / count
    print(ans)