How to index JavaScript deserialize method in asp.net MVC?

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I am trying to do something like this:

JavaScriptSerializer js = new JavaScriptSerializer();
Session["token"] = js.Deserialize<dynamic>(HtmlResult)[0];

My variable HtmlResult Contains Json Object and have three fields.

{
  "access_token": "0mlMO3RHjFN0DzUzIyok7XhOHXAj-J1id-dnL1rFQF9aWr4DJxCB1u9pd6LI7NkAIzf8qKKeDP-kN-Uk5ND-rsSoNUtlB1lZxGGx7ytVa2CoJdd1iZzHxJLkLXJep481AbeT1iyU45kjj8IaldIghREBTgGqjBrX9U0MpHy455Ac_hO6O0t78wXGl0AIjxWKt3N7cfpXE-Thhirda75Sd5ogiODc-p85Rtw76w61Lsc",
  "token_type": "bearer",
  "expires_in": 86399
}

I want to access only the first and second field i.e. access_token and token_type and store them in variable seprately only if the return Json data has these three property . how i can do it.