What was the percentage change in net periodic benefit cost from 2018 to 2019?
{"Service cost": {"2019": 162, "2018": 250, "2017": 313}, "Interest cost": {"2019": 1740, "2018": 1687, "2017": 1901}, "Expected return on plan assets": {"2019": -375, "2018": -926, "2017": -843}, "Recognized actuarial loss": {"2019": 777, "2018": 1392, "2017": 1182}, "Net periodic benefit cost": {"2019": 2304, "2018": 2403, "2017": 2553}}
net_periodic_benefit_cost_2019 = df["Net periodic benefit cost"]["2019"]
net_periodic_benefit_cost_2018 = df["Net periodic benefit cost"]["2018"]
answer = (net_periodic_benefit_cost_2019 - net_periodic_benefit_cost_2018) / net_periodic_benefit_cost_2018 * 100.0