using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        string input = "TEST";

         //string -> string

        var reversed = new List<char>();

​

        for (int i = input.Length; i < 0; i--)

        {

            reversed.Add(input[i]);

        }

​

        Console.WriteLine(reversed.ToString());

    }

}