using System;
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(){
XPathDocument document = new XPathDocument("books.xml");
XPathNavigator navigator = document.CreateNavigator();
XPathNodeIterator nodes = navigator.Select("//book");
XPathExpression query = nodes.Current.Compile("sum(descendant::price)");
Double total = (double)navigator.Evaluate(query, nodes);
Console.WriteLine("Total price for all books: {0}", total.ToString());
}
}