Input (grade 12): He regained the world # 1 ranking again in October 2008, and officially remained # 1 until January 2010, when he fell to # 2 behind Carlsen.
Output (grade 12): He regained the world # 1 ranking again in October 2008, and officially remained # 1 until January 2010, when he fell to # 2 behind Magnus Carlsen.