03. Memory game

using System;
using System.Collections.Generic;
using System.Linq;

namespace Program
{
    class Program
    {
        static void Main(string[] args)
        {

             List<string> list = Console.ReadLine().Split().ToList();


            string input = string.Empty;
                int counter = 0;
                bool end = false;
            while ((input=Console.ReadLine())!="end")
            {
                string[] command = input.Split();
                string firstIndex = command[0];
                string secondIndex = command[1];
                int startIndex =int.Parse(firstIndex);
                int endIndex = int.Parse(secondIndex);
                if (list.Count==0||list.Count==1)
                    {
                     end = true;
                Console.WriteLine($"You have won in {counter} turns!");
                    break;
                    }
                if (startIndex < 0 || startIndex >= list.Count)
                {
                    Console.WriteLine("Invalid input! Adding additional elements to the board");
                    counter++;
                    string added = "-" + counter + "a";
                    list.Insert(list.Count / 2, added);
                    list.Insert(list.Count / 2, added);

                }
                else if (endIndex < 0 || endIndex >= list.Count)
                {
                    Console.WriteLine("Invalid input! Adding additional elements to the board");
                    counter++;
                    string added = "-" + counter + "a";
                    list.Insert(list.Count / 2, added);
                    list.Insert(list.Count / 2, added);

                }
                else if(startIndex == endIndex)
                {
                    Console.WriteLine("Invalid input! Adding additional elements to the board");
                    counter++;
                    string added = "-" + counter + "a";
                    list.Insert(list.Count / 2, added);
                    list.Insert(list.Count / 2, added);
                }
                else
                {

                         counter ++;
                        if (list[startIndex]==list[endIndex])
                        {
                            Console.WriteLine($"Congrats! You have found matching elements - {list[startIndex]}!");
                        if (firstIndex=="0")
                        {
                            list.Remove(list[startIndex]);
                            list.Remove(list[endIndex-1]);
                        }
                        else
                        {
                            list.Remove(list[startIndex]);
                            list.Remove(list[endIndex]);
                        }

                        }
                        else Console.WriteLine("Try again!");
                }
            }
            if (end==false)
            {
                Console.WriteLine($"Sorry you lose :(");
                Console.WriteLine(String.Join(" ", list));
            }

        }
    }
}