Puzzle of the Day 6 January 2017 |  Find the best move

1. Rb7+ Kc4 2. Ka7 a5 3. Kb6 a4 4. Ka5 a3 5. Ka4 a2 6. Rc7+ Kd3 7. Rc1 a1=Q+ 8. Rxa1 Kc2 9. Kb5 Kb2 10. Ra8 Kb1 11. Ra7 Kb2 12. Ra6 Kb1 13. Ra5 Kb2 14. Ra4 Kc2