Exam 7. Longest Alphabetical Word

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Threading;

public class LongestAlphabeticalWord
{
    public static void Main()
    {
        Thread.CurrentThread.CurrentCulture = CultureInfo.InvariantCulture;
        checked
        {
            string inputWord = Console.ReadLine();
            int length = int.Parse(Console.ReadLine());

            string longestWord = inputWord[0].ToString();
            if (length > 1)
            {
                char[,] matrix = new char[length, length];
                int indexInString = 0;
                for (int row = 0; row < length; row++)
                {
                    for (int col = 0; col < length; col++)
                    {
                        matrix[row, col] = inputWord[(indexInString % inputWord.Length)];
                        indexInString++;
                    }
                }

                List<string> wordsList = new List<string>();
                for (int row = 0; row < length; row++)
                {
                    for (int col = 0; col < length; col++)
                    {
                        string rightWord = FindAlphabeticalWord(matrix, length, row, col, 0, 1);
                        wordsList.Add(rightWord);

                        string leftWord = FindAlphabeticalWord(matrix, length, row, col, 0, -1);
                        wordsList.Add(leftWord);

                        string downWord = FindAlphabeticalWord(matrix, length, row, col, 1, 0);
                        wordsList.Add(downWord);

                        string upperWord = FindAlphabeticalWord(matrix, length, row, col, -1, 0);
                        wordsList.Add(upperWord);
                    }
                }

                wordsList.Sort();
                int countLetters = 0;
                foreach (string word in wordsList)
                {
                    if (word.Length > countLetters)
                    {
                        countLetters = word.Length;
                        longestWord = word;
                    }
                }
            }

            Console.WriteLine(longestWord);
        }
    }

    private static string FindAlphabeticalWord(char[,] matrix, int length, int row, int col, int directY, int directX)
    {
        checked
        {
            string word = string.Empty + matrix[row, col];
            char previous = matrix[row, col];
            while (true)
            {
                row += directY;
                col += directX;
                bool isInMatrix = row >= 0 && row < length && col >= 0 && col < length;
                if (!isInMatrix || matrix[row, col] <= previous)
                {
                    break;
                }

                word += matrix[row, col];
                previous = matrix[row, col];
            }

            return word;
        }
    }
}