{"pre_text": ["table of contents valero energy corporation notes to consolidated financial statements ( continued ) 11 .", "equity share activity activity in the number of shares of common stock and treasury stock was as follows ( in millions ) : common treasury ."], "post_text": ["preferred stock we have 20 million shares of preferred stock authorized with a par value of $ 0.01 per share .", "no shares of preferred stock were outstanding as of december 31 , 2018 or 2017 .", "treasury stock we purchase shares of our common stock as authorized under our common stock purchase program ( described below ) and to meet our obligations under employee stock-based compensation plans .", "on july 13 , 2015 , our board of directors authorized us to purchase $ 2.5 billion of our outstanding common stock with no expiration date , and we completed that program during 2017 .", "on september 21 , 2016 , our board of directors authorized our purchase of up to an additional $ 2.5 billion with no expiration date , and we completed that program during 2018 .", "on january 23 , 2018 , our board of directors authorized our purchase of up to an additional $ 2.5 billion ( the 2018 program ) with no expiration date .", "during the years ended december 31 , 2018 , 2017 , and 2016 , we purchased $ 1.5 billion , $ 1.3 billion , and $ 1.3 billion , respectively , of our common stock under our programs .", "as of december 31 , 2018 , we have approval under the 2018 program to purchase approximately $ 2.2 billion of our common stock .", "common stock dividends on january 24 , 2019 , our board of directors declared a quarterly cash dividend of $ 0.90 per common share payable on march 5 , 2019 to holders of record at the close of business on february 13 , 2019 .", "valero energy partners lp units on september 16 , 2016 , vlp entered into an equity distribution agreement pursuant to which vlp offered and sold from time to time their common units having an aggregate offering price of up to $ 350 million based on amounts , at prices , and on terms determined by market conditions and other factors at the time of ."], "table": [["", "commonstock", "treasurystock"], ["balance as of december 31 2015", "673", "-200 ( 200 )"], ["transactions in connection withstock-based compensation plans", "2014", "1"], ["stock purchases under purchase program", "2014", "-23 ( 23 )"], ["balance as of december 31 2016", "673", "-222 ( 222 )"], ["transactions in connection withstock-based compensation plans", "2014", "1"], ["stock purchases under purchase programs", "2014", "-19 ( 19 )"], ["balance as of december 31 2017", "673", "-240 ( 240 )"], ["stock purchases under purchase programs", "2014", "-16 ( 16 )"], ["balance as of december 31 2018", "673", "-256 ( 256 )"]], "table_ori": [["", "CommonStock", "TreasuryStock"], ["Balance as of December 31, 2015", "673", "(200)"], ["Transactions in connection withstock-based compensation plans", "—", "1"], ["Stock purchases under purchase program", "—", "(23)"], ["Balance as of December 31, 2016", "673", "(222)"], ["Transactions in connection withstock-based compensation plans", "—", "1"], ["Stock purchases under purchase programs", "—", "(19)"], ["Balance as of December 31, 2017", "673", "(240)"], ["Stock purchases under purchase programs", "—", "(16)"], ["Balance as of December 31, 2018", "673", "(256)"]]}

Question: how much , in billions , was spent purchasing common stock under the programs from 2016-2018?
Evidence:
text_8: during the years ended december 31 , 2018 , 2017 , and 2016 , we purchased $ 1.5 billion , $ 1.3 billion , and $ 1.3 billion , respectively , of our common stock under our programs .
Program: add(1.5, 1.3), add(#0, 1.3)
Answer:
str_answer: 4.1
exe_answer: 4.1