how to get value from json result calling by ajax method

$.ajax({
    type: "POST",
    url:'@Url.Action("Shortlist", "Search")' ,
    dataType: "json",
    data: '{candidateid: "' + shortlistid + '" }',                
    contentType: "application/json",
    success: function (response) {
        alert(response.data);
    }
})

[HttpPost]
public JsonResult Shortlist(string candidateid)
{
    string output = "User Shortlisted";
    return Json(output,JsonRequestBehavior.AllowGet);
}