Ads integration to working android game

It is a simple and fast job. This is my game: [login to view URL] I will give you full source code. It is working. You need to use android studio. I have "pretio" ads on game exit. I want to integrate appodeal ads on play button. If you download and use game you will see, game loading on first screen. Then user press play button to play game. Now on first screen or second screen (playing screen) if I press back button app exits. I want it on second screen if I press back button app must be return to first screen and show appodeal interstitial ads. Then I press again to exit app this time it will show pretio ads. All appodeal integration and pretio integration work, I just need back functionality between first and second screen. And stabilization of the app, delete unused and correct warning. Simple job, I will have another jobs like that, and you will have all the sources so price it low. Thanks