What was the change in the basic shares used in per share calculation between 2017 and 2018?
{"Consolidated Statements of Operations Data:                     -- Net revenues": {"2019": 995789.0, "2018": 983142.0, "2017": 607084.0, "2016": 519834.0, "2015": 552940.0}, "Consolidated Statements of Operations Data:                     -- Operating income (loss) (1)": {"2019": -14726.0, "2018": -38210.0, "2017": 6040.0, "2016": -30029.0, "2015": -62994.0}, "Consolidated Statements of Operations Data:                     -- Net loss": {"2019": -25853.0, "2018": -46792.0, "2017": -1744.0, "2016": -36363.0, "2015": -71643.0}, "Consolidated Statements of Operations Data:                     -- Net loss per share  basic": {"2019": -0.22, "2018": -0.41, "2017": -0.02, "2016": -0.35, "2015": -0.72}, "Consolidated Statements of Operations Data:                     -- Net loss per share  diluted": {"2019": -0.22, "2018": -0.41, "2017": -0.02, "2016": -0.35, "2015": -0.72}, "Consolidated Statements of Operations Data:                     -- Shares used in per share calculation  basic": {"2019": 117954.0, "2018": 114221.0, "2017": 108273.0, "2016": 103074.0, "2015": 99000.0}, "Consolidated Statements of Operations Data:                     -- Shares used in per share calculation  diluted": {"2019": 117954.0, "2018": 114221.0, "2017": 108273.0, "2016": 103074.0, "2015": 99000.0}}
basic_shares_2018 = df["Consolidated Statements of Operations Data:                     -- Shares used in per share calculation  basic"]["2018"]
basic_shares_2017 = df["Consolidated Statements of Operations Data:                     -- Shares used in per share calculation  basic"]["2017"]
answer = basic_shares_2018 - basic_shares_2017