Puzzle of the Day 10 March 2021 |  Find the best move

1. ... Rc8+ 2. Kb5 Kd3 3. Ka6 Kxd2 4. b5 Kxc3 5. b6 Ra8+ 6. Kb5 Rb8 7. Kc6 Kc4 8. Kc7 Re8