public ActionResult Admin_Login(Users user)
        {
            if (ModelState.IsValid)
            {
                int ID = UsersBL.CheckExistentUser(user);
                if (ID == 0)
                {
                    ModelState.AddModelError("UserID", "UserName or Password is Error");
                    return(RedirectToAction("Admin"));
                }
                else if (ID == 1)
                {
                    return(RedirectToAction("Doctors"));
                }
                else if (ID == 2)
                {
                    return(RedirectToAction("students"));
                }
            }

            return(View(user));
        }