What was the change in employee stock options between 2018 and 2019?
{"Anti-dilutive securities: -- Employee stock options": {"January 31, 2020": 34, "February 1, 2019": 50, "February 2, 2018": 51}, "Anti-dilutive securities: -- Restricted stock units": {"January 31, 2020": 315, "February 1, 2019": 255, "February 2, 2018": 140}, "Anti-dilutive securities: -- Total": {"January 31, 2020": 349, "February 1, 2019": 305, "February 2, 2018": 191}}
antidilutive_securities__employee_stock_options_february_1_2019 = df["Anti-dilutive securities: -- Employee stock options"]["February 1, 2019"]
antidilutive_securities__employee_stock_options_february_2_2018 = df["Anti-dilutive securities: -- Employee stock options"]["February 2, 2018"]
answer = antidilutive_securities__employee_stock_options_february_1_2019 - antidilutive_securities__employee_stock_options_february_2_2018