replace string function

See more:

C#

ASP.NET

I am trying to remove brackets () and name "tag", from the following string: Tag (5174102)

This is what I am using but when I add the following line of code , I get a blank page/null. Hence , I can, so far remove the "tag" string.
href = Regex.Replace(href, "[^a-zA-Z]", "");

public static string readUri2()
        {
            string uri = "";
            var document = XDocument.Parse(WRequest());
            var href = document.Descendants("link").Single().Attribute("title").Value;
            href = href.Replace("Tag", "");
            href = Regex.Replace(href, "[^a-zA-Z]", "");
            return uri = href.ToString();
			
			}

My desired output is to get, only the number from the above string.
Any hints in, how can I achieve this, please. Many thanks