XML C#

using System;
using System.IO;
using System.Linq;
using System.Xml;
using System.Xml.Linq;
using System.Collections;
using System.Collections.Generic;
using System.Xml.XPath;
public class MainClass
{
    public static void Main()
    {
        XmlDocument document = new XmlDocument();
        document.Load("domainBooks.xml");
        XPathNavigator navigator = document.CreateNavigator();
        navigator.MoveToChild("bookstore", "http://www.domain.com/books");
        navigator.MoveToChild("book", "http://www.domain.com/books");
        navigator.MoveToChild("price", "http://www.domain.com/books");
        navigator.InsertAfter("100");
        navigator.MoveToParent();
        Console.WriteLine(navigator.OuterXml);
    }
}