public function store(CreateCenterRequest $request)
 {
     $center = new ExamCenter();
     $center->fill($request->only('name', 'students_limit', 'lang', 'lat'))->save();
     $message = trans('exams::centers.create_success');
     if ($request->input('submit') == 'save') {
         return redirect()->route('exams.centers.create')->with('success', $message);
     }
     return redirect()->route('exams.centers.index')->with('success', $message);
 }