problem upload file in mvc

@using (Ajax.BeginForm("addfilezamimeh","letter", new { id = 90 }, new AjaxOptions { HttpMethod = "post", UpdateTargetId = "divAjax", InsertionMode = InsertionMode.Replace }, new { enctype = "multipart/form-data" }))
{                                             <input type="file" id="filex" />
                                             
                                            <input type="submit" value="nnnnnnnnnn"  />           
                                           <div id="divAjax"></div>
                        
}   

 [HttpPost]
        public ActionResult addfilezamimeh(int id,HttpPostedFileBase filex)
        
        {
            
          
            foreach (string upload in Request.Files)
            {
}
}