How to jump in frames?


I have animation and in animation I have two bottoms. One for move foward and wann to move back.
Now, I wanna to jump in frames, like, if i push buttom fwd, animation will go to next frame,if i push back, it will go back.


In layer1 you have animation from 1 to 15, then layer2 from 16 to 30.
Now, i have to jump from 1 to 15 and 16 to 30. and from 30 to 16 and 15 to 1 if I push back buttom.

Please help!