Yes, it is generally okay to do rough work without explicitly writing "Rough" at the top, as long as it is done in the designated rough space or margins provided in the answer sheet. However, in some exams, invigilators may require you to label rough work to avoid confusion. To be sure, it's best to follow the exam guidelines or ask the invigilator before starting. Always ensure that rough work does not mix with the final answers to avoid any issues during evaluation.