What is the percentage change in 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}}
allowance_2019 = df["Allowance for doubtful accounts, ending balance"]["December 31, 2019"]
allowance_2018 = df["Allowance for doubtful accounts, beginning balance"]["December 31, 2019"]
answer = (allowance_2019 - allowance_2018) / allowance_2018 * 100.0