using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        string input = "TEST_TEXT_ONE_20112017";

        Console.WriteLine(RemoveDate(input));

        Console.WriteLine(RemoveDateFixedLength(input));

    }

    private static string RemoveDate(string input)

    {

        string[] parts = input.Split('_');

        return string.Join("_", parts.Take(parts.Length - 1));

    }

    private static string RemoveDateFixedLength(string input)

    {

        //Removes last 9 characters (8 for date, 1 for underscore)

        return input.Substring(0, input.Length - 9);

    }

}