note 9 : shareholders 2019 equity common stock under the dividend reinvestment and direct stock purchase plan ( the 201cdrip 201d ) , shareholders may reinvest cash dividends and purchase additional company common stock , up to certain limits , through the plan administrator without commission fees . shares purchased by participants through the drip may be newly issued shares , treasury shares , or at the company 2019s election , shares purchased by the plan administrator in the open market or in privately negotiated transactions . purchases generally will be made and credited to drip accounts once each week . as of december 31 , 2018 , there were approximately 4.2 million shares available for future issuance under the drip . anti-dilutive stock repurchase program in february 2015 , the company 2019s board of directors authorized an anti-dilutive stock repurchase program , which allowed the company to purchase up to 10 million shares of its outstanding common stock over an unrestricted period of time . the company repurchased 0.6 million shares and 0.7 million shares of common stock in the open market at an aggregate cost of $ 45 million and $ 54 million under this program for the years ended december 31 , 2018 and 2017 , respectively . as of december 31 , 2018 , there were 5.5 million shares of common stock available for purchase under the program. .
intangible asset amortization expense amounted to $ 12 million , $ 4 million and $ 4 million for the years ended december 31 , 2018 , 2017 and 2016 , respectively . estimated amortization expense for the next five years subsequent to december 31 , 2018 is as follows: .
at what price per share did awk repurchase its shares of common stock in 2017?
the company repurchased 0.6 million shares and 0.7 million shares of common stock in the open market at an aggregate cost of $ 45 million and $ 54 million under this program for the years ended december 31 , 2018 and 2017 , respectively .
amount
2019 $ 15
2020 13
2021 11
2022 10
2023 7