For Postretirement health plans, what is the percentage constitution of interest cost among the net periodic benefit cost in 2017?
{"Qualified Plan: -- Interest cost": {"2019": 19825, "2018": 19463, "2017": 19889}, "Qualified Plan: -- Expected return on plan assets": {"2019": -26334, "2018": -26467, "2017": -26811}, "Qualified Plan: -- Actuarial loss": {"2019": 2754, "2018": 3331, "2017": 4455}, "Qualified Plan: -- Net periodic benefit credit": {"2019": -3755, "2018": -3673, "2017": -2467}, "SERP: -- Service cost": {"2019": "$\u2014", "2018": 490, "2017": 855}, "SERP: -- Interest cost": {"2019": 3080, "2018": 2894, "2017": 2850}, "SERP: -- Actuarial loss": {"2019": 1207, "2018": 1538, "2017": 1659}, "SERP: -- Amortization of unrecognized prior service cost": {"2019": 115, "2018": 146, "2017": 153}, "SERP: -- Net periodic benefit cost": {"2019": 4402, "2018": 5068, "2017": 5517}, "Postretirement health plans: -- Interest cost": {"2019": 997, "2018": 955, "2017": 1003}, "Postretirement health plans: -- Actuarial (gain) loss": {"2019": -159, "2018": -27, "2017": 162}, "Postretirement health plans: -- Net periodic benefit cost": {"2019": 838, "2018": 928, "2017": 1165}}
interest_cost_2017 = df["Postretirement health plans: -- Interest cost"]["2017"]
net_periodic_benefit_cost_2017 = df["Postretirement health plans: -- Net periodic benefit cost"]["2017"]
answer = interest_cost_2017 / net_periodic_benefit_cost_2017 * 100.0