What is the increase/ (decrease) in Gross profit from the period December 31, 2018 to 2019?
{"": {"December 31, 2019": "", "September 29, 2018": "(Unaudited, in millions)", "December 31, 2018": "", "Sequential": "", "Year-Over-Year": ""}, "Gross profit": {"December 31, 2019": 1081.0, "September 29, 2018": 967.0, "December 31, 2018": 1059.0, "Sequential": 11.8, "Year-Over-Year": 2.0}, "Gross margin (as percentage of net revenues)": {"December 31, 2019": 39.3, "September 29, 2018": 37.9, "December 31, 2018": 40.0, "Sequential": 140.0, "Year-Over-Year": -70.0}}
gross_profit_2019 = df["Gross profit"]["December 31, 2019"]
gross_profit_2018 = df["Gross profit"]["December 31, 2018"]
answer = gross_profit_2019 - gross_profit_2018