public static void Main()
@"<body><h1>This is <b>bold</b> heading</h1><p>This is <u>underlined</u> paragraph</p></body>";
var htmlDoc = new HtmlDocument();
var htmlBody = htmlDoc.DocumentNode.SelectSingleNode("//body");
HtmlNode firstChild = htmlBody.FirstChild;
Console.WriteLine(firstChild.OuterHtml);