using System;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
      string s = "## I am `testing` ~~something~~ _that_ *is* [a](https://google.com)";
      string pattern = "([*_~#`]|http)";
      string replacement = "\\$1";
      
      Regex rgx = new Regex(pattern);
      string t = rgx.Replace(s, replacement);

      Console.WriteLine("Original String: {0}", s);
      Console.WriteLine("Replacement String: {0}", t);  
	}
}