Eva and Mark played badminton and Viktor counted the exchanges. After every 10 exchanges, Viktor drew a cross (X). Then, instead of every 10 crosses, he drew a circle (O) and erased the corresponding 10 crosses. When Eva and Mark finished the game, Viktor had drawn the following:

## OOOXXXXXXX

Determine the minimum and maximum number of exchanges Eva and Mark played.

(M. Smitková)

Hint. How many exchanges could Eva and Mark have played if only one circle was drawn at the end?
Each circle replaces 10 křř̌̌uْ, the previous notation thus corresponds to 37 křř̌̌ks. Each křřžek represents 10 played exchanges, so Eva and Mark played at least 370 and at most 379 exchanges.

#