using System;

public class Program

{

        public static void Main()

        {

            var array = "tettstttt".ToCharArray();

            var arrayLastIndex = array.Length - 1;

            var toIterateIndex = arrayLastIndex;

            var polyndromeCheckIndex = GetEqualItemIndex(array, arrayLastIndex);

            if (polyndromeCheckIndex > 0)

            {

                toIterateIndex = polyndromeCheckIndex;

            }

​

            for (int i = 0; i < arrayLastIndex; i++)

                Console.Write(array[i]);

            for (int i = toIterateIndex; i >= 0; i--)

                Console.Write(array[i]);

            Console.ReadLine();

        }

​

        private static int GetEqualItemIndex(char[] array, int index)

        {

            var checkResult = -1;

            var compareElement = array[index];

            for (int i = 0; i <= index; i++)

            {

                if (array[i] == compareElement && IsPolyndrome(array,i,index))

                {                   

                    checkResult = i;

                    break;

                }

            }

            return checkResult;

        }

​

​

        private static bool IsPolyndrome(char[] array, int startIndex, int endIndex)

        {

            var result = true;

            var endtIter = endIndex;

            for (int i = startIndex; i <= endIndex; i++)

            {

                if (array[i] != array[endtIter])

                {

                    result = false;

                    break;

                }

                endtIter--;

            }

            return result;

        } 

}