What is the change in the net foreign exchange gains and losses between 2018 and 2017?
{"Financial income and expenses -- SEK million": {"2018": 2018, "2017": 2017}, "Reported in prior years -- Reported in prior years": {"2018": 316, "2017": 372}, "Reported in prior years -- Financial expenses": {"2018": 2389, "2017": 843}, "Reported in prior years -- Total": {"2018": 2705, "2017": 1215}, "Reported in prior years -- SEK million": {"2018": 2018, "2017": 2017}, "Restated -- Financial income": {"2018": 151, "2017": 50}, "Restated -- Financial expenses": {"2018": 2032, "2017": 1570}, "Restated -- Net foreign exchange gains and losses": {"2018": 824, "2017": 405}, "Restated -- Total": {"2018": -2705, "2017": 1215}}
net_foreign_exchange_gains_and_losses_2018 = df["Restated -- Net foreign exchange gains and losses"]["2018"]
net_foreign_exchange_gains_and_losses_2017 = df["Restated -- Net foreign exchange gains and losses"]["2017"]
answer = - net_foreign_exchange_gains_and_losses_2018 - net_foreign_exchange_gains_and_losses_2017