rules of Catchup

I think the rules are pretty simple:

1. a group is considered as bunch of touching stones.2. Each player can drop 2 stones on an empty field turnwise with following exceptions:2a the first move you only get 1 one stone2b if the biggest group after the previous move is bigger than the biggest group before the previous move you get 3 stones. except the first turn of the second player.3. the winner is the player with the largest group at the end. In case of ties forget the largest and look at the next largest, and so on.(the is always solvable as the are 6k+1 places to drop a stone.

Correction: you always have the option to play 1 or 2 stones on your turn.

The site hasn't implemented that correctly (and there's a bug in the tiebreaker, as well).

So a player either has the option to put 1 or 2 stones or is forced to put 3 stones (in case the opponent increased the size of the largest group)!?

Or is the 3 stone option an option in the sense that a player is allowed to put less than three stones, e.g. just 1 or 2?