What was the change in balance as of January 1 between 2018 and 2019?
{"Balance as of January 1,": {"2019": 282.4, "2018": 131.0, "2017": 45.9}, "Current year increases": {"2019": 104.3, "2018": 157.8, "2017": 87.2}, "Write-offs, recoveries and other (1)": {"2019": -223.4, "2018": -6.4, "2017": -2.1}, "Balance as of December 31,": {"2019": 163.3, "2018": 282.4, "2017": 131.0}}
balance_as_of_january_1_2019 = df["Balance as of January 1,"]["2019"]
balance_as_of_january_1_2018 = df["Balance as of January 1,"]["2018"]
answer = balance_as_of_january_1_2019 - balance_as_of_january_1_2018