#カードゲーム
#https://yukicoder.me/problems/199
from itertools import permutations

N = int(input())
A = list(map(int, input().split()))
B = list(map(int, input().split()))
A_perm = list(permutations(A))
B_perm = list(permutations(B))
ans = 0
for a in A_perm:
    for b in B_perm:
        awin = 0
        bwin = 0
        for an,bn in zip(a,b):
            if an > bn:
                awin += 1
            else:
                bwin += 1
        if awin > bwin:
            ans += 1
print(ans/(len(A_perm)*len(B_perm)))