import sys
import numpy as np
#from numba import njit, b1, i1, i4, i8, f8, jitclass
sys.setrecursionlimit(10**9)
from itertools import permutations

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

def input(): return sys.stdin.readline().strip()
#"""
def from_read(dtype=np.int64):
    return np.fromstring(read().decode(), dtype=dtype, sep=' ')

def from_readline(dtype=np.int64):
    return np.fromstring(readline().decode(), dtype=dtype, sep=' ')
#"""

        
#@njit("(i8,i8,i8,i8[:],i8[:],)", cache=True)
def main(N, A, B):
    total = 1
    for i in range(1, N + 1): total *= i
    total *= total
    ans = 0
    for a in permutations(A, N):
        for b in permutations(B, N):
            win = 0
            for aa, bb in zip(a, b):
                win += 1 if aa > bb else 0
            ans += 1 if win > N // 2 else 0
    print(ans / total)
            

if __name__ == '__main__':
    N = int(input())
    A = from_readline()
    B = from_readline()
    main(N, A, B)