What was the change in the Beginning balance between 2017 and 2018?
{"Beginning balance": {"2019": 436.0, "2018": 398.5, "2017": 220.7}, "Increases related to acquisitions": {"2019": 329.7, "2018": "\u2014", "2017": 193.3}, "Decreases related to settlements with tax authorities": {"2019": -8.3, "2018": -0.1, "2017": -11.7}, "Decreases related to statute of limitation expirations": {"2019": -16.2, "2018": -10.9, "2017": -7.6}, "Increases related to current year tax positions": {"2019": 27.8, "2018": 30.3, "2017": 26.3}, "Increases (decreases) related to prior year tax positions": {"2019": -5.6, "2018": 18.2, "2017": -22.5}, "Ending balance": {"2019": 763.4, "2018": 436.0, "2017": 398.5}}
beginning_balance_2018 = df["Beginning balance"]["2018"]
beginning_balance_2017 = df["Beginning balance"]["2017"]
answer = beginning_balance_2018 - beginning_balance_2017