using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Xml;
using System.Xml.Serialization;

namespace Kurs
{

    [XmlRoot("tabela_kursow")]
    public class XmlData
    {
        [XmlElement("pozycja")]
        public List<pozycja> Currencies { get; set; }
    }

    public class pozycja
    {
        public string nazwa_waluty { get; set; }
        public string przelicznik { get; set; }
        public string kod_waluty { get; set; }
        public string kurs_sredni { get; set; }
        public double GetValue()
        {
            return double.Parse(kurs_sredni.Replace(',', '.'));
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            String URLString = "http://www.nbp.pl/Kursy/XML/LastA.xml";
            XmlTextReader reader = new XmlTextReader(URLString);
            var ser = new XmlSerializer(typeof(XmlData));
            XmlData data = (XmlData)ser.Deserialize(reader);
            double price = data.Currencies.Find(i => i.kod_waluty.Equals("USD")).GetValue();
            System.Console.WriteLine(price.ToString());
            System.Console.ReadKey();
        }
    }
}