What is the total software value as at December 31, 2018 and 2019?
{"Equipment": {"Useful life (in years)": 1, "December 31, 2019": 22702, "December 31, 2018": 49804}, "Software": {"Useful life (in years)": 1, "December 31, 2019": 726, "December 31, 2018": 4088}, "Furniture and fixtures": {"Useful life (in years)": 1, "December 31, 2019": 459, "December 31, 2018": 967}, "Leasehold improvements": {"Useful life (in years)": 2, "December 31, 2019": 5440, "December 31, 2018": 3832}, "Construction in progress": {"Useful life (in years)": "", "December 31, 2019": "--", "December 31, 2018": 160}, "Property and equipment, gross": {"Useful life (in years)": "", "December 31, 2019": 29327, "December 31, 2018": 58581}, "Less: accumulated depreciation": {"Useful life (in years)": "", "December 31, 2019": -21671, "December 31, 2018": -51589}, "Property and equipment, net": {"Useful life (in years)": "", "December 31, 2019": 7656, "December 31, 2018": 7262}}
software_2019 = df["Software"]["December 31, 2019"]
software_2018 = df["Software"]["December 31, 2018"]
answer = software_2019 + software_2018