This is pretty easy game.
All you have to do is that u need to choose if ur A or B. A counts -1 and B counts +1. And then we start from 100.
And it should look like this:
Player1: A 99
Player2: B 100
Player1: A 99
Player3: A 98
Player4: A 97
Player1: A 96
Player2: B 97
Player5: B 98
And so on....
So i start and i am A
A 99
