导航栏后退按钮更改功能

I have 3 view controllers: A, B and C. A is initial and it has 2 buttons: one is redirecting to B, and second one to C. When B is pushed, and button within B pressed user is redirected to C. Now on navigation bar within C, when I press back button I want to be redirected to A always, and never to B. Is that possible?I have 3 view controllers: A, B and C. A is ini