What was the change in gross profit in 2019 from 2018?
{"Reconciliation to revenue -- Revenue": {"2019": 692.6, "2018": 635.4, "2017": 657.0}, "Reconciliation to revenue -- Port expenses, bunkers and commissions": {"2019": -267.7, "2018": -283.0, "2017": -259.9}, "Reconciliation to revenue -- Charter hire": {"2019": "-", "2018": -2.5, "2017": -8.5}, "Reconciliation to revenue -- Operating expenses": {"2019": -173.0, "2018": -180.4, "2017": -188.4}, "Reconciliation to revenue -- Gross profit": {"2019": 251.9, "2018": 169.5, "2017": 200.2}}
gross_profit_2019 = df["Reconciliation to revenue -- Gross profit"]["2019"]
gross_profit_2018 = df["Reconciliation to revenue -- Gross profit"]["2018"]
answer = gross_profit_2019 - gross_profit_2018