Sto utilizzando Newtonsoft Json per deserializzare la risposta di una chiamata ad un'API di OpenWeather Map, ma ricevo questo errore quando eseguo la pagina:

Newtonsoft.Json.JsonReaderException: 'Unexpected character encountered while parsing value: S. Path '', line 0, position 0.'

Cosa sbaglio? Ecco il codice:

codice:
public partial class Default1 : System.Web.UI.Page
    {


        public class Main
        {
            public double temp { get; set; }
            public double temp_min { get; set; }
            public double temp_max { get; set; }
            public double pressure { get; set; }
            public double sea_level { get; set; }
            public double grnd_level { get; set; }
            public int humidity { get; set; }
            public double temp_kf { get; set; }
        }


        public class Weather
        {
            public int id { get; set; }
            public string main { get; set; }
            public string description { get; set; }
            public string icon { get; set; }
        }


        public class Clouds
        {
            public int all { get; set; }
        }


        public class Wind
        {
            public double speed { get; set; }
            public double deg { get; set; }
        }


        public class Snow
        {
            public double? __invalid_name__3h { get; set; }
        }


        public class Sys
        {
            public string pod { get; set; }
        }


        public class List
        {
            public int dt { get; set; }
            public Main main { get; set; }
            public List<Weather> weather { get; set; }
            public Clouds clouds { get; set; }
            public Wind wind { get; set; }
            public Snow snow { get; set; }
            public Sys sys { get; set; }
            public string dt_txt { get; set; }
        }


        public class Coord
        {
            public double lat { get; set; }
            public double lon { get; set; }
        }


        public class City
        {
            public int id { get; set; }
            public string name { get; set; }
            public Coord coord { get; set; }
            public string country { get; set; }
        }


        public class RootObject
        {
            public string cod { get; set; }
            public double message { get; set; }
            public int cnt { get; set; }
            public List<List> list { get; set; }
            public City city { get; set; }
        }


        public class Account
        {
            public string Email { get; set; }
            public bool Active { get; set; }
            public DateTime CreatedDate { get; set; }
            public IList<string> Roles { get; set; }
        }


        public class Deserializza
        {
            public string Active { get; set; }
            public string Email { get; set; }
        }


        protected void Page_Load(object sender, EventArgs e)
        {
            Account account = new Account
            {
                Active = true,
                Email = "miaMail@tiscali.it"
            };


            string json = JsonConvert.SerializeObject(account, Formatting.Indented);








            Deserializza deserializza = JsonConvert.DeserializeObject<Deserializza>(json);
            




           WebRequest request = WebRequest.Create("https://samples.openweathermap.org/data/2.5/forecast?id=524901&appid=mioAppID");
            request.ContentType = "application/json";
            WebResponse response = request.GetResponse();
            string jsonRicevuto = response.ToString();
            Main main = JsonConvert.DeserializeObject<Main>(jsonRicevuto);
            double prova = main.pressure;


        }






    }
Sto cercando di familiarizzare con Json, quindi accetto ogni consiglio.