A summary of the outstanding shares of common stock is as follows:



Balance as of January 1, 2013	824,297,756
Exercise of stock options	2,777,127
Issuance of restricted stock	146,848
Forfeiture of unvested restricted stock	(13,076	)
Repurchase of common stock	(8,570,281	)
Exercise of warrants	64,562
Balance as of December 31, 2013	818,702,936
Exercise of stock options	1,955,108
Issuance of restricted stock	31,137
Vesting of restricted stock units	29,541
Forfeiture of unvested restricted stock	(8,675	)
Repurchase of common stock	(22,451,875	)
Balance as of December 31, 2014	798,258,172
Exercise of stock options	688,743
Issuance of restricted stock	49,438
Vesting of restricted stock units	34,750
Forfeiture of unvested restricted stock	(2,000	)
Repurchase of common stock	(4,383,793	)
Balance as of December 31, 2015	794,645,310