using System;
     
    namespace For39262
    {
        internal class Program
        {
            private static void Main(string[] args)
            {
                Console.WriteLine("Here we go...");
     
                int[] A = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 };
                int K = 3;
     
                TaskNo1 taskNo1 = new TaskNo1(A, K);
     
                try
                {
                    int[] result = taskNo1.GetResult();
                    for (int i = 0; i < result.Length; i++)
                    {
                        Console.WriteLine(result[i]);
                    }
                    Console.WriteLine("Extracted elements: "
                                      + result.Length + "/" + A.Length);
                }
                catch (TaskException ex)
                {
                    Console.WriteLine(ex.Message);
                }
     
                Console.Read();
            }
     
            public class TaskNo1
            {
                public readonly int[] A;
                public readonly int N;
                public readonly int K;
     
                public TaskNo1(int[] a, int k)
                {
                    A = a;
                    K = k;
                    N = A.Length;
                }
     
                public int[] GetResult()
                {
                    // Проверка уловия для K
                    if (!IsInitialСonditionsSatisfied())
                        throw new TaskException("K is wrong");
     
                    // Определение длины массива для результата
                    int lengthOfResult = 0;
                    for (int i = 1; i <= N; i++)
                    {
                        if (isAmultipleFor(i, K))
                        {
                            lengthOfResult++;
                        }
                    }
     
                    int[] result = new int[lengthOfResult];
     
                    // Заполнение массива резульатами
                    int resultCounter = 0;
                    for (int i = 1; i <= N; i++)
                    {
                        if (isAmultipleFor(i, K))
                        {
                            int realIndex = i - 1;
                            result[resultCounter] = A[realIndex];
                            resultCounter++;
                        }
                    }
     
                    return result;
                }
     
                public bool IsInitialСonditionsSatisfied()
                {
                    if (K < 1)
                        return false;
     
                    if (K > N)
                        return false;
     
                    return true;
                }
     
                public bool isAmultipleFor(int a, int b)
                {
                    return a % b == 0;
                }
            }
     
            internal class TaskException : ApplicationException
            {
                public TaskException(string message)
                    : base(message)
                {
                }
            }
        }
    }