What is the change in Basic weighted average common shares outstanding from year ended December 31, 2018 to 2019?
{"Net income attributable to ON Semiconductor Corporation": {"2019": 211.7, "2018": 627.4, "2017": 810.7}, "Basic weighted average common shares outstanding": {"2019": 410.9, "2018": 423.8, "2017": 421.9}, "Add: Incremental shares for: -- Dilutive effect of share-based awards": {"2019": 1.9, "2018": 4.3, "2017": 5.5}, "Add: Incremental shares for: -- Dilutive effect of convertible notes": {"2019": 3.2, "2018": 7.8, "2017": 0.9}, "Add: Incremental shares for: -- Diluted weighted average common shares outstanding": {"2019": 416.0, "2018": 435.9, "2017": 428.3}, "Net income per common share attributable to ON Semiconductor Corporation: -- Basic": {"2019": 0.52, "2018": 1.48, "2017": 1.92}, "Net income per common share attributable to ON Semiconductor Corporation: -- Diluted": {"2019": 0.51, "2018": 1.44, "2017": 1.89}}
basic_weighted_average_common_shares_outstanding_2019 = df["Basic weighted average common shares outstanding"]["2019"]
basic_weighted_average_common_shares_outstanding_2018 = df["Basic weighted average common shares outstanding"]["2018"]
answer = basic_weighted_average_common_shares_outstanding_2019 - basic_weighted_average_common_shares_outstanding_2018