What is the total value of stock options in 2018 and 2019?
{"Year Ended December 31 -- ": {"2019": 2019, "2018": 2018}, "Year Ended December 31 -- Common stock, vested at issuance and nonvested at issuance": {"2019": 721, "2018": 555}, "Year Ended December 31 -- Stock options": {"2019": 354, "2018": 132}, "Year Ended December 31 -- Restricted stock units": {"2019": 225, "2018": 103}, "Year Ended December 31 -- Compensation expense related to common stock awards issued under equity incentive plan": {"2019": 1300, "2018": 790}}
year_ended_december_31__stock_options_2019 = df["Year Ended December 31 -- Stock options"]["2019"]
year_ended_december_31__stock_options_2018 = df["Year Ended December 31 -- Stock options"]["2018"]
answer = year_ended_december_31__stock_options_2019 + year_ended_december_31__stock_options_2018