To buy chips with four No. 1-18 (1 lose 1), three chips to buy 25-36 number (1 lose 2), a coin to buy 19,20,22,23 (1 lose 8).
So, if you open it will play No. 1-18, and (chance 18/37), opened 19,20,22,23,25-36 win a coin (chance 16/37), opened 0,21,24 on the PK ( chance 3 / 37).
This approach is only open three numbers will lose one.