using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace YukiCoder2
{
    class Program
    {
        public static bool NextPermutation<T>(T[] array, int start, int length)
            where T : IComparable
        {
            int end = start + length - 1;

            if (end <= start) return false;

            int last = end;
            while (true)
            {
                int pos = last--;

                if (array[last].CompareTo(array[pos]) < 0)
                {
                    int i;
                    for (i = end + 1; array[last].CompareTo(array[--i]) >= 0; ) { }
                    T tmp = array[last]; array[last] = array[i]; array[i] = tmp;
                    Array.Reverse(array, pos, end - pos + 1);
                    return true;
                }
                if (last == start)
                {
                    Array.Reverse(array, start, end - start);
                    return false;
                }
            }

            throw new Exception("NextPermutation: Fatal error");
        }

        static void Main(string[] args)
        {
            var line = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
            var n = line[0];
            var aCards = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
            var bCards = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
            int sum = 0;
            do
            {
                var bCopy = bCards.ToArray();
                do
                {
                    int win = 0;
                    for (int i = 0; i < n; i++)
                    {
                        if (aCards[i] > bCards[i])
                        {
                            win++;
                        }
                    }
                    if (win > n / 2)
                    {
                        sum++;
                    }
                    
                } while (NextPermutation(bCopy, 0, n));
            } while (NextPermutation(aCards, 0, n));

            Console.WriteLine(sum/(double)(n*n));
        }
    }
}