Changes in common stock during the periods presented were as follows (amounts and shares in millions):



	Common Stock
	Shares		Amount
			(At par)
Balance at August 31, 2017	53.5		$	0.5
Issuance of restricted stock grants, net of cancellations	0.2		—
Stock options exercised	—	*	—
Balance at August 31, 2018	53.7		$	0.5
Issuance of restricted stock grants, net of cancellations	0.1		—
Balance at August 31, 2019	53.8		$	0.5
Issuance of restricted stock grants, net of cancellations	0.1		—
Stock options exercised	—	*	—
Balance at August 31, 2020	53.9		$	0.5

As of August 31, 2020 and 2019, we had 15.0 million and 14.3 million of repurchased shares recorded as treasury stock at an original repurchase cost of $1.23 billion and $1.16 billion, respectively.

In March 2018, the Board authorized the repurchase of up to six million shares of common stock. As of August 31, 2020, 2.1 million shares had been purchased under this authorization, of which 0.7 million were repurchased in fiscal 2020. The maximum number of shares that may yet be purchased under the program as of August 31, 2020 equaled 3.9 million shares.

We have 50 million shares of preferred stock authorized. No shares of preferred stock were issued in fiscal 2020 or 2019, and no shares of preferred stock are outstanding.

Basic earnings per share for the periods presented is computed by dividing net earnings available to common stockholders by the weighted average number of common shares outstanding for these periods. Diluted earnings per share is computed similarly but reflects the potential dilution that would occur if dilutive options were exercised, all unvested share-based payment awards were vested, and other distributions related to deferred stock agreements were incurred.

The following table calculates basic earnings per common share and diluted earnings per common share during the periods presented (in millions, except per share data):



	Year Ended August 31,
	2020		2019		2018
Net income	$	248.3	$	330.4	$	349.6
Basic weighted average shares outstanding	39.5		39.7		40.9
Common stock equivalents	0.1		0.1		0.1
Diluted weighted average shares outstanding	39.6		39.8		41.0
Basic earnings per share	$	6.29	$	8.32	$	8.54
Diluted earnings per share	$	6.27	$	8.29	$	8.52

The following table presents stock options, restricted stock awards, and performance share units that were excluded from the diluted earnings per share calculation for the periods presented as the effect of inclusion would have been antidilutive:



	Year Ended August 31,
	2020	2019	2018
Stock options	598,000	300,000	179,000
Restricted stock awards	213,000	160,000	227,000
Performance stock units *	—	—	—

* Represents shares of less than 1,000 in fiscal 2020. No performance stock units awards were outstanding in fiscal 2019 or fiscal 2018.