using System;

using System.Collections.Specialized;

public class Program

{

    public static void Main()

    {

        NameValueCollection value = System.Web.HttpUtility.ParseQueryString("");

        System.Console.WriteLine(value.AllKeys.Length.ToString());

        foreach(string v1 in value.AllKeys){

            System.Console.WriteLine(v1);

                                     }

    }

}