What was the change in the net periodic pension cost between 2018 and 2019?
{"Service cost": {"2019": 272, "2018": 841, "2017": "$  \u2014"}, "Interest cost": {"2019": 1211, "2018": 802, "2017": 809}, "Expected return on plan assets": {"2019": -615, "2018": -665, "2017": -597}, "Amortization of actuarial gains and losses": {"2019": 411, "2018": 478, "2017": 503}, "Net periodic pension cost": {"2019": 1279, "2018": 1456, "2017": 715}}
net_periodic_pension_cost_2019 = df["Net periodic pension cost"]["2019"]
net_periodic_pension_cost_2018 = df["Net periodic pension cost"]["2018"]
answer = net_periodic_pension_cost_2019 - net_periodic_pension_cost_2018