using System;

public class Program

{

    public static void Main()

    {

           Console.WriteLine("введите а ");

            double a = double.Parse(Console.ReadLine());

            Console.WriteLine("введите n ");

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

            double s = 0;

            for (double k = 1; k <= n; k++)

            {

                s = s + Math.Pow(a, k);

​

            }

            Console.WriteLine("ответ");

            Console.WriteLine(s); 

            Console.ReadKey();

​

        }

}