Draw a triangle and label the vertices 1~2~3.
Place a coin or button on the corner labelled '1'.
Call the score to be 1. This is a single ~ shared ~ score ~ it is not owned by either player.
The first player moves the marker to either of the other two corners and adjusts the score by adding 2 or 3.
The second player moves the marker and adjusts the score accordingly.
The person successfully moving the marker and exactly reaching the score of 12 wins the game.