using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Collections.Generic;
using System.Diagnostics;
using Enu = System.Linq.Enumerable;

class Program
{
    public void Solve()
    {
        int N = Reader.Int();
        double PA = Reader.Double(), PB = Reader.Double();
        int[] A = Reader.IntArray(N), B = Reader.IntArray(N);
        var sw = Stopwatch.StartNew();
        Array.Sort(A); Array.Sort(B);
        var ProbA = GetProb(N, PA);
        Array.Clear(bitdp, 0, bitdp.Length);
        var ProbB = GetProb(N, PB);
        double ans = 0;

        for (int ai = 0; ai < N; ai++)
            for (int bi = 0; bi < N; bi++)
                if (A[ai] > B[bi])
                    for (int pos = 0; pos < N; pos++)
                        ans += (A[ai] + B[bi]) * ProbA[ai, pos] * ProbB[bi, pos];

        Console.WriteLine(ans);
        //Console.WriteLine(sw.ElapsedMilliseconds);
        //Console.WriteLine(GC.GetTotalMemory(false).ToString("n0"));
        //Console.ReadLine();
    }

    double[] bitdp = new double[(1 << 20) * 20 + 20];
    double[,] GetProb(int N, double selectMinProb)
    {
        bitdp[0] = 1;
        var res = new double[N, N]; // i, at

        for (int mask = 0; mask < (1 << N); mask++)
        {
            int num = BitCount(mask);
            int rem = N - num;
            int min = -1;
            double currProb = 0;
            for (int i = 0; i < N; i++)
            {
                currProb += bitdp[mask * N + i];
                if (min == -1 && (mask >> i & 1) == 0) min = i;
            }
            for (int next = 0; next < N; next++)
                if ((mask >> next & 1) == 0)
                {
                    double selectProb = (rem == 1) ? 1 : (next == min) ? selectMinProb : (1 - selectMinProb) / (rem - 1);
                    double p = currProb * selectProb;
                    bitdp[(mask | 1 << next) * N + next] += p;
                    res[next, num] += p;
                }
        }
        return res;
    }

    int BitCount(int x) { return x == 0 ? 0 : 1 + BitCount(x & x - 1); }
}



class Entry { static void Main() { new Program().Solve(); } }
class Reader
{
    private static TextReader reader = Console.In;
    private static readonly char[] separator = { ' ' };
    private static readonly StringSplitOptions op = StringSplitOptions.RemoveEmptyEntries;
    private static string[] A = new string[0];
    private static int i;
    private static void Init() { A = new string[0]; }
    public static void Set(TextReader r) { reader = r; Init(); }
    public static void Set(string file) { reader = new StreamReader(file); Init(); }
    public static bool HasNext() { return CheckNext(); }
    public static string String() { return Next(); }
    public static int Int() { return int.Parse(Next()); }
    public static long Long() { return long.Parse(Next()); }
    public static double Double() { return double.Parse(Next()); }
    public static int[] IntLine() { return Array.ConvertAll(Split(Line()), int.Parse); }
    public static int[] IntArray(int N) { return Enu.Range(0, N).Select(i => Int()).ToArray(); }
    public static int[][] IntTable(int H) { return Enu.Range(0, H).Select(i => IntLine()).ToArray(); }
    public static string[] StringArray(int N) { return Enu.Range(0, N).Select(i => Line()).ToArray(); }
    public static string Line() { return reader.ReadLine().Trim(); }
    private static string[] Split(string s) { return s.Split(separator, op); }
    private static string Next() { CheckNext(); return A[i++]; }
    private static bool CheckNext()
    {
        if (i < A.Length) return true;
        string line = reader.ReadLine();
        if (line == null) return false;
        if (line == "") return CheckNext();
        A = Split(line);
        i = 0;
        return true;
    }
}