What was the change in cash proceeds between 2018 and 2019?
{"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}}
cash_proceeds_february_1_2019 = df["Cash proceeds"]["February 1, 2019"]
cash_proceeds_february_2_2018 = df["Cash proceeds"]["February 2, 2018"]
answer = cash_proceeds_february_1_2019 - cash_proceeds_february_2_2018