using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Bài 67: Tính S(x, n) = x – x^2 + x^3 + … + (-1)^n+1 * x^n");

        Console.WriteLine("Nhap vao so x:");

        int x=int.Parse(Console.ReadLine());

        Console.WriteLine("Nhap vao so n:");

        int n=int.Parse(Console.ReadLine());

        double s=0;

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

        {   

            s+= Math.Pow(-1,i+1)* Math.Pow(x,i);    

        }

        Console.WriteLine("Ket qua la:{0}",s);

    }

}