How to Retrieve HTML Input Text thru Code Behind Using C#?

 
Hi,  
I tried to retrieve the value of an HTML input text box but unable...   Any suggestion?   Below is the html and the code behind.   <asp:Content ID="Content3" ContentPlaceHolderID="mainPH" Runat="Server">  
  <input readonly="readonly" type="Text" id="txtName"/>  
<asp:Content>< ...