using System; 

using System.Text.RegularExpressions; 

using System.Collections.Generic;

class Program 

{ 

    static char[] alphabet = { 'a', 'b', 'c' }; 

    static List<string> GenerateWords(int n) 

    { 

        List<string> words = new(); 

        int alphabetSize = alphabet.Length; 

        int[] indices = new int[n]; 

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

        { 

            // Convert index to base-alphabet and append corresponding letters 

            string word = ""; 

            int index = i; 

            while (index > 0) 

            { 

                int remainder = index % alphabetSize; 

                word = alphabet[remainder] + word; 

                index /= alphabetSize; 

            } 

            while (word.Length < 1) 

            { 

                word = alphabet[0] + word; 

            } 

            Console.WriteLine(word); 

            words.Add(word); 

        } 

        return words; 

    } 

    static void FindRegex(List<string> words, string finalChars) 

    { 

        string regex = "^("; 

        for (int i = 0; i <alphabet.Length; i++) 

        { 

            regex += alphabet[i]; 

            if (i != alphabet.Length - 1) regex += '|'; 

        } 

        regex += ")+(" + finalChars+")$"; 

        Console.WriteLine("Regular expression: " + regex); 

        List<string> matchingWords = new List<string>(); 

        foreach (string word in words) 

        { 

            if (Regex.IsMatch(word, regex)) 

            { 

                matchingWords.Add(word); 

            } 

        } 

        if (matchingWords.Count == 0) Console.WriteLine("Words not found or final symbols are not contained in this alphabet"); 

        else 

        { 

            Console.WriteLine("Matching words: "); 

            foreach (string word in matchingWords) 

            { 

                Console.WriteLine(word); 

            } 

        } 

    } 

    static void Main(string[] args) 

    { 

        List<string> words= GenerateWords(30); 

        FindRegex(words, "cc");   

    }  

}