At January 1, 2017, Elan Corporation had 300,000 common shares outstanding (no preferred issued). On March 1, the corporation issued 45,000 new shares to raise additional capital. On July 1, the corporation declared and issued a 2 for 1 stock split. On October 1, the corporation purchased on the open market 180,000 of its own shares at $35 each and retired them.

Required : Calculate the weighted average number of common shares outstanding to be used in calculating earnings per share for 2017.