using System;

using System.Linq; 

using System.Collections.Generic;

using System.Text.RegularExpressions; 

public class Program

{

    public static void Main()

    {

         string text = @"{ 

            ""_id"" : ObjectId(""5a676641ecd0a32a385f61bb""), 

            ""find"" : {

                ""$Event.Alert.State"" : false

            }, 

            ""update"" : {

                ""$set"" : {

                    ""State"" : 0

                }

            }

        } ";

         Console.WriteLine(MongoEncode(text));

    }

    public static string MongoEncode(string JSON)

    {

        string tmpJSON;

        //From $ To #

        string pattern = @"([,{]\s*"")(\$)(.+""\s*:)";

        JSON = Regex.Replace(JSON, pattern, m => m.Groups[1].Value + "#" + m.Groups[3].Value); 

        //From . To #

        pattern = @"([,{]\s*"".+)(\.)(.+""\s*:)";

        do {

         tmpJSON = JSON;

         JSON = Regex.Replace(JSON, pattern, m => m.Groups[1].Value + "#" + m.Groups[3].Value);

        } while (tmpJSON!=JSON) ;

        return JSON;

    }

}