using System;

​

public class Program

{

    public static string GetInnermostString(string input, string startDelimiter, string endDelimiter)

    {

        if (string.IsNullOrEmpty(input) || string.IsNullOrEmpty(startDelimiter) || string.IsNullOrEmpty(endDelimiter))

            return null;

​

        int innermostStart = -1;

        int innermostEnd = -1;

        int nestingLevel = 0;

        int maxNestingLevel = 0;

​

        for (int i = 0; i < input.Length - startDelimiter.Length + 1; i++)

        {

            if (input.Substring(i, startDelimiter.Length) == startDelimiter)

            {

                nestingLevel++;

                if (nestingLevel > maxNestingLevel)

                {

                    maxNestingLevel = nestingLevel;

                    innermostStart = i;

                }

                i += startDelimiter.Length - 1;

            }

            else if (i <= input.Length - endDelimiter.Length && 

                     input.Substring(i, endDelimiter.Length) == endDelimiter)

            {

                nestingLevel--;

                i += endDelimiter.Length - 1;

            }

        }

​

        if (innermostStart == -1 || nestingLevel != 0)

            return null;

​

        nestingLevel = 0;

        for (int i = innermostStart; i < input.Length - endDelimiter.Length + 1; i++)

        {

            if (input.Substring(i, startDelimiter.Length) == startDelimiter)

            {

                nestingLevel++;

                i += startDelimiter.Length - 1;

            }

            else if (input.Substring(i, endDelimiter.Length) == endDelimiter)

            {

                nestingLevel--;

                if (nestingLevel == 0)

                {

                    innermostEnd = i + endDelimiter.Length;

                    break;

                }

                i += endDelimiter.Length - 1;

            }

        }

​

        if (innermostEnd == -1)

            return null;

​

        return input.Substring(innermostStart + startDelimiter.Length, 

                               innermostEnd - innermostStart - startDelimiter.Length - endDelimiter.Length);

    }

​

    // Example usage

    public static void Main()

    {   

        Console.WriteLine("Grok AI Generated Code for GetInnermostString function"); 

        //string test1pass = "Hello <!--world <!--inner--> text--> outside";

        string test1fail = "<!--Hello <!--world <!--inner--> text--> outside"; //unbalance delimeters, first

        //string test2pass = "Hello <!--world <!--inner--> text--> outside-->"; //unbalance delimeters, last

        Console.WriteLine(GetInnermostString(test1fail, "<!--", "-->")); // Outputs: "inner"

    }

}