# N<=4なので全探索可能
# Nが大きいときはどうやってやるんだろうね

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

from itertools import permutations
A_win = 0
total = 0
for b_combo in permutations(B, N):
    #print(b_combo)
    total += 1
    temp = 0
    for i in range(N):
        if A[i] > b_combo[i]:
            temp += 1
    if temp > N//2:
        A_win += 1
ans = A_win/total
print(ans)