What is the difference in the balances for derivative contracts for 31 January 2018 and 31 January 2019?
{"Balances, January 31, 2018": {"Derivative Contracts": 1.0, "Convertible Debt Securities": 7.8, "Total": 8.8}, "Settlements": {"Derivative Contracts": "\u2014", "Convertible Debt Securities": -3.5, "Total": -3.5}, "(Losses) Gains included in earnings (1)": {"Derivative Contracts": -0.2, "Convertible Debt Securities": 0.5, "Total": 0.3}, "Losses included in OCI": {"Derivative Contracts": "\u2014", "Convertible Debt Securities": -0.4, "Total": -0.4}, "Balances, January 31, 2019": {"Derivative Contracts": 0.8, "Convertible Debt Securities": 4.4, "Total": 5.2}}
balance_january_31_2018_derivative = df["Balances, January 31, 2018"]["Derivative Contracts"]
balance_january_31_2019_derivative = df["Balances, January 31, 2019"]["Derivative Contracts"]
answer = balance_january_31_2018_derivative - balance_january_31_2019_derivative