using System;
using System.Linq;

namespace CardGame_CS
{
    class Program
    {
        static void Main(string[] args)
        {
            Solver sol = new Solver();
            sol.Solve();
        }
    }

    class Solver
    {
        int N;
        int[] A;
        int[] B;
        bool[] used;
        int win = 0;
        int[] AP;

        public void Solve()
        {
            Action<int> CountWin = null;
            CountWin = n =>
            {
                if (n == N)
                {
                    int Lwin = AP.Zip(B, (a, b) => a > b).Count(e=>e);
                    int Llose = N - Lwin;
                    if (Lwin > Llose) win++;
                    return;
                }
                for (int i = 0; i < N; i++)
                {
                    if (!used[i])
                    {
                        AP[n] = A[i];
                        used[i] = true;
                        CountWin(n + 1);
                        used[i] = false;
                    }
                }
            };

            CountWin(0);

            int factN = 1;
            for (int i = 1; i <= N; i++) factN *= i;

            double ans = (double)win / factN;
            Console.WriteLine(ans);
        }

        public Solver()
        {
            N = ri();
            A = ria();
            B = ria();
            AP = new int[N];
            used = new bool[N];
        }

        static String rs() { return Console.ReadLine(); }
        static int ri() { return int.Parse(Console.ReadLine()); }
        static long rl() { return long.Parse(Console.ReadLine()); }
        static double rd() { return double.Parse(Console.ReadLine()); }
        static String[] rsa() { return Console.ReadLine().Split(' '); }
        static int[] ria() { return Console.ReadLine().Split(' ').Select(e => int.Parse(e)).ToArray(); }
        static long[] rla() { return Console.ReadLine().Split(' ').Select(e => long.Parse(e)).ToArray(); }
        static double[] rda() { return Console.ReadLine().Split(' ').Select(e => double.Parse(e)).ToArray(); }
    }
}