What is the Balance at beginning of period expressed as a percentage of Balance at end of period for year 2019?
{"Balance at beginning of period(1)": {"2019": 150.1, "2018": 71.5}, "Gains (losses) on assets still held at end of year": {"2019": 16.8, "2018": -16.0}, "Purchases, sales, issuance, and settlements(2)": {"2019": 8.3, "2018": 103.7}, "Transfers in and/or out of Level 3": {"2019": "\u2014", "2018": 1.0}, "Foreign exchange gain (loss)": {"2019": 5.0, "2018": -10.1}, "Balance at end of period(1)": {"2019": 180.2, "2018": 150.1}}
balance_at_beginning_of_period1_2019 = df["Balance at beginning of period(1)"]["2019"]
balance_at_end_of_period1_2019 = df["Balance at end of period(1)"]["2019"]
answer = balance_at_beginning_of_period1_2019 / balance_at_end_of_period1_2019 * 100.0