What is the sum of the 2 highest gross carrying amounts?
{"2021 Notes": {"Gross Carrying Amount": 650, "Unamortized Discount and Deferred Financing Costs": -2, "Net Carrying Amount": 648}, "2022 Notes": {"Gross Carrying Amount": 400, "Unamortized Discount and Deferred Financing Costs": -2, "Net Carrying Amount": 398}, "2026 Notes": {"Gross Carrying Amount": 850, "Unamortized Discount and Deferred Financing Costs": -7, "Net Carrying Amount": 843}, "2027 Notes": {"Gross Carrying Amount": 400, "Unamortized Discount and Deferred Financing Costs": -5, "Net Carrying Amount": 395}, "2047 Notes": {"Gross Carrying Amount": 400, "Unamortized Discount and Deferred Financing Costs": -9, "Net Carrying Amount": 391}, "Total debt": {"Gross Carrying Amount": 2700, "Unamortized Discount and Deferred Financing Costs": -25, "Net Carrying Amount": 2675}}
gross_2026 = df["2026 Notes"]["Gross Carrying Amount"]
gross_2021 = df["2021 Notes"]["Gross Carrying Amount"]
answer = max(gross_2026, gross_2021) + min(gross_2026, gross_2021)