Hi thanks for query, I understand your expectations towards examination, requirement of hardwork and concentration. but you also need to think how much stress and pressure you are undergoing. when there is lot of pressure and stress gradually there will be decrease in concentration. its not the pill will help you rather than intake of good nutritious food and sleep will keep you calm and increase your concentration. you need to work on subject matter rather than expecting on the result. if you are scared of the result you can never perform better. try to focus on self and your expectations. take care wish you the best. you can take help of psychologist to deal with your stress.