/************************************************
Grundlegende Algorithmen mit Java,
http://algorithmen-und-problemloesungen.de/
Copyright @2007-2008 by Doina Logofatu

in C#: Michael Gärtner
************************************************/

using System;
using System.IO;

namespace Logofatu
{
    class P7Equation
    {
        private static String FileInputName = "equation.in";
        private static String FileOutputName = "equation.out";
        private static IFormatProvider formatProvider = 
            System.Globalization.CultureInfo.GetCultureInfo("en-US").NumberFormat;

        private static double sum(int n, double s, double p)
        {
            if ( 0 == n )
                return 2;
            if ( 1 == n )
                return s;
            return s * sum(n - 1, s, p) - p * sum(n - 2, s, p);
        }

        static void Main(string[] args)
        {
            StreamReader sr = null;
            StreamWriter sw = null;
            try
            {
                sr = new StreamReader(FileInputName);
                sw = new StreamWriter(FileOutputName);

                while ( !sr.EndOfStream )
                {
                    string[] sArray = sr.ReadLine().Split(' ');
                    int n = int.Parse(sArray[0],formatProvider);
                    double s = double.Parse(sArray[1],formatProvider);
                    double p = double.Parse(sArray[2],formatProvider);
                    sw.WriteLine(sum(n, s, p).ToString("g6", formatProvider));
                }
            }
            catch ( IOException ex )
            {
                Console.WriteLine("Fehler bei der Dateiverarbeitung!\n" + ex);
            }
            finally
            {
                if ( sr != null )
                {
                    sr.Close();
                }
                if ( sw != null )
                {
                    sw.Close();
                }
            }
        }
    }
}