from Queue import * # Queue, LifoQueue, PriorityQueue
from bisect import * #bisect, insort
from collections import * #deque, Counter,OrderedDict,defaultdict
#set([]) 
import math
import copy
import itertools
import string
import sys
myread = lambda : map(int,raw_input().split())
def solver():
    N = int(raw_input())
    A = myread()
    B = myread()
    cnt = 0
    all_cnt = 0
    for a in itertools.permutations(A):
        for b in itertools.permutations(B):
            all_cnt += 1
            win = 0
            for i in xrange(N):
                win += a[i] > b[i]
            if win > (N/2):
                cnt += 1
    print "%.10f" % (float(cnt)/all_cnt)
if __name__ == "__main__":
    solver()