What was the average Change in valuation allowance for 2017-2019?
{"Income tax benefit at the US Federal statutory rate": {"2019": -2718, "2018": -3654, "2017": -4019}, "Benefit for state taxes": {"2019": -304, "2018": -642, "2017": -142}, "Impact of foreign operations": {"2019": -310, "2018": 38, "2017": 158}, "Indefinite life assets": {"2019": 130, "2018": 335, "2017": 102}, "Officer life insurance": {"2019": 3, "2018": -5, "2017": -6}, "Change in valuation allowance": {"2019": 3302, "2018": 3328, "2017": 4007}, "Change in liability for unrecognized tax benefits": {"2019": -400, "2018": 40, "2017": 9}, "Impact of Tax Act, net": {"2019": 226, "2018": -3287, "2017": "\u2014"}, "Meals and entertainment": {"2019": 60, "2018": 81, "2017": 163}, "Equity": {"2019": 2, "2018": 476, "2017": "\u2014"}, "Global intangible low-taxed income": {"2019": 94, "2018": "\u2014", "2017": "\u2014"}, "Other": {"2019": 136, "2018": 39, "2017": -36}, "Total income tax expense (benefit)": {"2019": 221, "2018": -3251, "2017": 236}}
change_in_valuation_allowance_2019 = df["Change in valuation allowance"]["2019"]
change_in_valuation_allowance_2018 = df["Change in valuation allowance"]["2018"]
change_in_valuation_allowance_2017 = df["Change in valuation allowance"]["2017"]
officer_life_insurance_2019 = df["Officer life insurance"]["2019"]
answer = ( change_in_valuation_allowance_2019 + change_in_valuation_allowance_2018 + change_in_valuation_allowance_2017 ) / officer_life_insurance_2019