using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var obj = new Cosma();

        var sum = obj.SumArray(new int[] { 0, 2, 1, 0, 4, 0, 0, 0, 8, 3, 0, 2, 6, 0, 0, 0, 3, 2, 0 });

        Console.WriteLine(sum.ToString());

    }

}

​

public class Cosma

    {

        public int SumArray(int[] values)

        {

            //Validations

            var arrayCount = values.Count();

            if (arrayCount < 1 || arrayCount > 1000000)

                throw new Exception("Array elements count must be in range of [1..1,000,000]");

            if (values.Max() > 9 || values.Min() < 0)

                throw new Exception("Array elements must be in range of [0..9]");

​

            //Processing logic

            long.TryParse(string.Join("", values.Reverse()), out long newValue);

            var product = (17 * newValue).ToString();

            var intCharArray = Array.ConvertAll(product.ToCharArray(), c => (int)char.GetNumericValue(c));

​

            return intCharArray.Sum();

        }

    }