using System;

public class Program

{

    public static void Main()

    {

        double x = Convert.ToDouble(Console.ReadLine());

        double n = Convert.ToDouble(Console.ReadLine());

        double p=1,p1=3,sum=0,sum1=0,fact=1,den,num,d=0;

        for(int i=0;i<n;i++)

        {

          if(i%2==0)

          {

              sum=sum+Math.Pow(x,p);

              p=p+4;

              num=sum;

          }

         else

            {

                sum1=sum1-Math.Pow(x,p1);

                p1=p1+4;

                 num=sum1;

            }

            for(int k=1;k<i+1;k++)

            {

                fact=fact*k;

            }

            den=fact;

             d = d+(num/den);

        }

        Console.WriteLine(d);

    }

}