How many diapers for NB and S sizes should I get?

My baby’s birth weight was only 2.6kg and it dipped abit for the first 1week and then started gaining on the 2nd. So I only used Just Born instead of New Born. It was up to 3.5kg which fits him better. So NB size I only got 1pack as his weight gain was drastic and went to S size now. Also different brands different size cutting. I think buy 1 pack try first better. Unless the offer very good then maybe can stock it up.