What was the change in the Balance - beginning of year from 2018 to 2019?
{"Balance - beginning of year": {"2019": 6795, "2018": 9410, "2017": 3279}, "Provision, net": {"2019": 11989, "2018": 15465, "2017": 29512}, "Charge-offs": {"2019": -13737, "2018": -18080, "2017": -23381}, "Balance - end of year": {"2019": 5047, "2018": 6795, "2017": 9410}}
balance__beginning_of_year_2019 = df["Balance - beginning of year"]["2019"]
balance__beginning_of_year_2018 = df["Balance - beginning of year"]["2018"]
answer = balance__beginning_of_year_2019 - balance__beginning_of_year_2018