What is the increase / (decrease) in the stock options from 2018 to 2019?
{"(In thousands of Canadian dollars)": {"2019": "$", "2018": "$"}, "Stock options": {"2019": 1046, "2018": 915}, "ISUs": {"2019": 61, "2018": 1}, "PSUs": {"2019": 981, "2018": 990}, "DSUs": {"2019": 631, "2018": "\u2014"}}
stock_options_2019 = df["Stock options"]["2019"]
stock_options_2018 = df["Stock options"]["2018"]
answer = stock_options_2019 - stock_options_2018