This is middle school math.
Untouched long side 10.4 blocks. That is, if you have a joint width of 2.7 cm, it fits evenly.
On the short sides, it becomes 6 blocks, which also fits evenly if you finish before the corner and have joints that are 4 cm. Maybe a bit large?
Broken long side gives 3.7 blocks on each side, so you likely won’t avoid having to cut there.
One round is thus 10+6+6+4+4=30, for the precision shopping list. When you actually build, it's probably easiest to make a scale drawing to get joints, etc., in suitable places.