What is the increase/ (decrease) in Balance at beginning of year from December 31, 2018 to 2019?
{"Balance at beginning of year": {"December 31, 2019": 38, "December 31, 2018": 333, "December 31, 2017": 258}, "Additions based on tax positions related to the current year": {"December 31, 2019": 7, "December 31, 2018": 43, "December 31, 2017": 43}, "Additions based on acquisitions related to the current year": {"December 31, 2019": 5, "December 31, 2018": "\u2014", "December 31, 2017": "\u2014"}, "Additions for tax positions of prior years": {"December 31, 2019": 1, "December 31, 2018": 8, "December 31, 2017": 12}, "Reduction for tax positions of prior years": {"December 31, 2019": -1, "December 31, 2018": -310, "December 31, 2017": -9}, "Settlements": {"December 31, 2019": -2, "December 31, 2018": -18, "December 31, 2017": -2}, "Prepayment / Refund": {"December 31, 2019": "\u2014", "December 31, 2018": "\u2014", "December 31, 2017": "\u2014"}, "Reductions due to lapse of statute of limitations": {"December 31, 2019": "\u2014", "December 31, 2018": "\u2014", "December 31, 2017": "\u2014"}, "Foreign currency translation": {"December 31, 2019": "\u2014", "December 31, 2018": -18, "December 31, 2017": 31}, "Balance at end of year": {"December 31, 2019": 48, "December 31, 2018": 38, "December 31, 2017": 333}}
balance_2019 = df["Balance at beginning of year"]["December 31, 2019"]
balance_2018 = df["Balance at beginning of year"]["December 31, 2018"]
answer = balance_2019 - balance_2018