using System;

using System.Xml;

using System.Xml.Linq;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var xml = @"<theFieldRoot>

   <group1>

      <field1></field1>

   </group1>

   <group2>

      <field2></field2>

      <group3>

         <field3></field3>

      </group3>

   </group2>

</theFieldRoot>";

        XmlDocument xmlDoc = new XmlDocument();

        xmlDoc.LoadXml(xml);

        XmlNode formSchema = xmlDoc.DocumentElement;

        int fields = formSchema.SelectNodes(".//*").Count;

        Console.WriteLine(fields);

    }

}