Send double value to MVC controller as a string

I've got an action in my controller

    [HttpGet]
    [Route("classificators/{type}/{criteria}/{predicate?}")]
    public ActionResult Classificators(string type, string criteria, string predicate)
    {
        try
        {
            //Lot's of cool code here!          

            return Json(new { Data = "Cool data!" }, JsonRequestBehavior.AllowGet);
        }
        catch (Exception ex)
        {
            return Json(new
            {
                state = "error",
                message = ExceptionReport(ex)
            }, JsonRequestBehavior.AllowGet);
        }
    }

And sending request to it like so..

/classificators/MAIN/CODE/50.1

Where: type - MAIN criteria - CODE predicate - 50.1

But action treats parametr 50.1 like double value so I've got an error. How to specify action to treat this value like a string