# https://qiita.com/drken/items/e77685614f3c6bf86f44
import itertools
import math

def main():
    n = int(input())
    a_list = list(map(int,input().split()))
    b_list = list(map(int,input().split()))

    cnt = 0
    for a_perm in itertools.permutations(a_list, n):
        for b_perm in itertools.permutations(b_list, n):
            a_win = 0
            for i in range(n):
                if a_perm[i]>b_perm[i]:
                    a_win += 1
            if a_win > n/2:
                cnt += 1
    # mathモジュールに階乗を返す関数factorial()
    print(cnt/math.factorial(n)/math.factorial(n))
if __name__ == '__main__':
    main()