using System;

using System.Text.RegularExpressions;

using System.Linq;

using System.Diagnostics;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        var json = @"{

              ""ID"" : ""1492"", 

              ""SourceID"" : ""AAA.A"",  

              ""Source"" : 1,

              ""SourceID"" : ""292"",

              ""Child"" : ""JKLM"",

              ""Name"" : ""KAPITAL YAT. "",

              ""ChildName"" : null, 

              ""ListingDate"" : ""20140428"", 

              ""SeqNo"" : ""10000000"", 

              ""Average"" : ""3092,3248"", 

              ""SomeValue"" : ""testValue""

            }";

        TestWithRegex(json);

        Console.WriteLine("\r\n\r\n");

        TestWithJsonConvert(json);

    }

    private static void TestWithRegex(string json)

    {

        var stopWatch = Stopwatch.StartNew();

        var pattern = @"(?<=\"")([^\s,].*?)(?=\"")|null";       

        var matches = Regex.Matches(json, pattern).OfType<object>().ToList();

        // Find Somevalue since it is last

        var index = matches.FindIndex(x => x.ToString() == "SomeValue");

        var val = matches[index + 1].ToString();

        Console.WriteLine("Index: " + index + " | Value: " + val);

        stopWatch.Stop();

        Console.WriteLine("Elapsed time with regex: " + stopWatch.ElapsedMilliseconds); 

    }

    private static void TestWithJsonConvert(string json)

    {

        var stopWatch = Stopwatch.StartNew();

        var obj = JsonConvert.DeserializeObject<Root>(json);

        Console.WriteLine("Value: " + obj.SomeValue);

        stopWatch.Stop();

        Console.WriteLine("Elapsed time with JsonConvert: " + stopWatch.ElapsedMilliseconds);

    }

    public class Root

    {

        public string ID { get; set; }

        public string SourceID { get; set; }

        public int Source { get; set; }

        public string Child { get; set; }

        public string Name { get; set; }

        public object ChildName { get; set; }

        public string ListingDate { get; set; }

        public string SeqNo { get; set; }

        public string Average { get; set; }

        public object SomeValue { get; set; }

    }

}