Another neat rook ending

Here is another lightweight ending, as I much prefer endings with few pieces, and even have quite a liking for lightweight endings without pawns (will try to show some of these soon).

White to play and win (as always, there is only one correct way to win)
In this one, white needs to try to promote a pawn, and if you need a hint, he sacrifices his rook, and then black is forced to return the favour (in fact black gets to promote while white doesn't!)

As promised, the solution to the previous ending (see below) is:
1. Kb8 Rb2+ 2. Ka8 Rc2 3. Rf6+ Ka5 4. Kb8 Rb2+ 5. Ka7 Rc2 6. Rf5+ Ka4 7. Kb7 Rb2+ 8. Ka6 Rc2 9. Rf4+ Ka3 10. Kb6 Rb2+ 11. Ka5 Rc2 12. Rf3+ Kb2 13. Rxf2 Rxf2 14. c8=Q

As always, comments are welcome, and I will try to reply if necessary.