Read a dynamically content from page in c#

Sir how to read dynamically content from page.Suppose i have a site and some tag like

 

Now i want to read data-id;

 

Please check my code:

 

WebClient x = new WebClient();

url = x.DownloadString("https://www.xyz.com/id='" + search.Text + "'");

Int32 data = url.IndexOf("data-id");


richTextBox1.Text += url.Substring(data , 170);