What is the total allowance for doubtful accounts, ending balance between 2018 and 2019?
{"Allowance for doubtful accounts, beginning balance": {"December 31, 2019": 319, "December 31, 2018": 983}, "Increase (decrease) of provision": {"December 31, 2019": -72, "December 31, 2018": -26}, "Write-offs": {"December 31, 2019": -195, "December 31, 2018": -638}, "Allowance for doubtful accounts, ending balance": {"December 31, 2019": 52, "December 31, 2018": 319}}
doubtful_accounts_allowance_ending_balance = df["Allowance for doubtful accounts, ending balance"]["December 31, 2019"]
doubtful_accounts_allowance_beginning_balance = df["Allowance for doubtful accounts, beginning balance"]["December 31, 2019"]
answer = doubtful_accounts_allowance_ending_balance + doubtful_accounts_allowance_beginning_balance