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

public class Test
{

	public static void Main()
	{ 
        string test = "test...abc...";
        string leftTrimmed = test.TrimLettersLeft();
        Console.WriteLine(test);
        Console.WriteLine(leftTrimmed);
	}
}

static class Exension
{
 public static string TrimLettersLeft(this string input)
        {
            int lastLetterIndex = -1;
            for (int i = input.Length - 1; i >= 0; i--)
            {
                if (Char.IsLetter(input[i]))
                {
                    lastLetterIndex = i;
                    break;
                }
            }

            if (lastLetterIndex == -1)
                return input;
            else
                return input.Substring(0, lastLetterIndex + 1);
        } 
}