What is the change in Cash, cash equivalents and restricted cash at beginning of period from December 31, 2019 to December 31, 2018?
{"Cash, cash equivalents and restricted cash at beginning of period": {"2019": 60068, "2018": 103051, "2017": 60765}, "Cash provided by operating activities": {"2019": 10317, "2018": 3295, "2017": 4863}, "Cash used in investing activities": {"2019": -24574, "2018": -48413, "2017": -70972}, "Cash provided by financing activities": {"2019": 494101, "2018": 3099, "2017": 108475}, "Effects of exchange rates on cash, cash equivalents and restricted cash": {"2019": -250, "2018": -964, "2017": -80}, "Cash, cash equivalents and restricted cash at end of period": {"2019": 539662, "2018": 60068, "2017": 103051}}
cash_2019 = df["Cash, cash equivalents and restricted cash at beginning of period"]["2019"]
cash_2018 = df["Cash, cash equivalents and restricted cash at beginning of period"]["2018"]
answer = cash_2019 - cash_2018