後ろから犯してから口の中で、それがセックスルーレット、どこでイクの?

I come home from college having invented a game called Sex Russian Roulette. My Stepdad has to face fuck me with 10 thrusts and then stop and fuck me from behind for 10 thrusts, and then swap again, but where and when will he cum, that is the question, in my mouth or from behind?