What was the change in Class A common stock purchased between 2019 and 2020?
{"Cash proceeds": {"January 31, 2020": 172.0, "February 1, 2019": 161.0, "February 2, 2018": 65.0}, "Class A common stock purchased": {"January 31, 2020": 1489.0, "February 1, 2019": 1895.0, "February 2, 2018": 903.0}, "Weighted-average price per share": {"January 31, 2020": 115.51, "February 1, 2019": 84.95, "February 2, 2018": 72.4}}
class_a_common_stock_purchased_january_31_2020 = df["Class A common stock purchased"]["January 31, 2020"]
class_a_common_stock_purchased_february_1_2019 = df["Class A common stock purchased"]["February 1, 2019"]
answer = class_a_common_stock_purchased_january_31_2020 - class_a_common_stock_purchased_february_1_2019