using System;

public class Program

{       

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

    {

        int startIndex = input.LastIndexOf(startDelimiter) + startDelimiter.Length;

        int endIndex = input.IndexOf(endDelimiter, startIndex);

​

        if (startIndex >= 0 && endIndex >= 0 && startIndex <= endIndex)

        {

            return input.Substring(startIndex, endIndex - startIndex);

        }

        return string.Empty; // or throw an exception if not found

    }

​

    public void Main()

    {

        // Example usage:

        //string text = "a(b(c)d)e"; // result will be "c", verified!

        //string text = "a(b(c)d)e)"; // test1

        string text = "(a(b(c)d)e"; // test2

        Console.WriteLine( GetInnermostString(text, "(", ")") ); // result will be "c"

    }

}