Passing input value to action (ASP.Net MVC 3)

I have code in View:

@using (Html.BeginForm("MyAction", "MyController")
{
    <input type="text" id="txt" />          
    <input type="image" src="/button_save.gif" alt="" />
}

How can I pass value of txt to my controller:

[HttpPost]
public ActionResult MyAction(string text)
{
 //TODO something with text and return value...
}