using System;
using System.Xml;

public class Test
{
	public static void Main()
	{
		var id = 3;
		var message = "&'<crazyMessage&&";

		var xmlDoc = new XmlDocument();
		
		using(var writer = xmlDoc.CreateNavigator().AppendChild())
		{
			writer.WriteStartElement("ROOT");
			
			writer.WriteElementString("ID", id.ToString());
			
			writer.WriteStartElement("INPUT");
			writer.WriteElementString("ENGMSG", message);
			writer.WriteEndElement(); // INPUT
			
			writer.WriteEndElement(); // ROOT
		}
		
		var xmlString = xmlDoc.InnerXml;
		Console.WriteLine(xmlString);
	}
}