import java.util.*;
public class ing {

    /**
     * @param args
     */
    public static void main(String[] args) {
        
        // TODO Auto-generated method stub
        double x;
        int n;
        double sum=0;
        ing m=new ing();
        Scanner sa=new Scanner(System.in );
        x= sa.nextDouble();
        n=sa.nextInt();
        if(String.valueOf(x)=="x"&&String.valueOf(n)=="n")
        {
            System.out.print("数列和");
        }
        else
        {
            sum=m.mypow(x, n)/m.fact(n);
            System.out.printf("%.4f",sum);
        }
    }
    /**
     *计算n的阶乘
     */
 public    double  fact(int n )
    {
        double sum=0;
        if(n==0)
        {
            sum=1;
        }
        else
        {
            sum=n*fact(n-1);
        }
        return sum ;
    }
    /**
     *计算x的n次幂
     */
  public double mypow(double x,int n)
  {
      double sum=0;
      sum=Math.pow(x, n)*Math.pow(-1, n-1);
      return sum;
  }

}