What is the change in Weighted-average shares used in computing basic net income per share from Fiscal Year Ended December 28, 2019 to December 29, 2018?
{"Weighted-average shares used in computing basic net income per share": {"December 28, 2019": 74994, "December 29, 2018": 73482, "December 30, 2017": 72292}, "Add potentially dilutive securities": {"December 28, 2019": 2292, "December 29, 2018": 1700, "December 30, 2017": 1947}, "Weighted-average shares used in computing basic and diluted net income per share": {"December 28, 2019": 77286, "December 29, 2018": 75182, "December 30, 2017": 74239}}
weighted_average_2019 = df["Weighted-average shares used in computing basic net income per share"]["December 28, 2019"]
weighted_average_2018 = df["Weighted-average shares used in computing basic net income per share"]["December 29, 2018"]
answer = weighted_average_2019 - weighted_average_2018