What is the total Prior service credits for the 3 years?
{"Defined benefit pension plans and other post-employment benefits: -- Prior service credits": {"2019": 0.1, "2018": 0.3, "2017": 1.3, "Location of Amount Reclassified from AOCL": ""}, "Defined benefit pension plans and other post-employment benefits: -- Actuarial losses": {"2019": -4.9, "2018": -3.1, "2017": -10.0, "Location of Amount Reclassified from AOCL": ""}, "Defined benefit pension plans and other post-employment benefits: -- Total pre-tax amount": {"2019": -4.8, "2018": -2.8, "2017": -8.7, "Location of Amount Reclassified from AOCL": "Other (expense) income, net"}, "Defined benefit pension plans and other post-employment benefits: -- Tax benefit": {"2019": 1.2, "2018": 0.7, "2017": 2.5, "Location of Amount Reclassified from AOCL": ""}, "Defined benefit pension plans and other post-employment benefits: -- Net of tax": {"2019": -3.6, "2018": -2.1, "2017": -6.2, "Location of Amount Reclassified from AOCL": ""}, "Net gains (losses) on cash flow hedging derivatives:(1) -- Foreign currency forward contracts": {"2019": 1.6, "2018": 0.2, "2017": 0.9, "Location of Amount Reclassified from AOCL": "Cost of sales"}, "Net gains (losses) on cash flow hedging derivatives:(1) -- Interest rate and currency swaps": {"2019": "\u2014", "2018": "\u2014", "2017": -3.4, "Location of Amount Reclassified from AOCL": ""}, "Net gains (losses) on cash flow hedging derivatives:(1) -- Treasury locks": {"2019": 0.1, "2018": 0.1, "2017": 0.1, "Location of Amount Reclassified from AOCL": "Interest expense, net"}, "Net gains (losses) on cash flow hedging derivatives:(1) -- Total pre-tax amount": {"2019": 1.7, "2018": 0.3, "2017": -2.4, "Location of Amount Reclassified from AOCL": ""}, "Net gains (losses) on cash flow hedging derivatives:(1) -- Tax (expense) benefit": {"2019": -0.6, "2018": -0.1, "2017": 0.8, "Location of Amount Reclassified from AOCL": ""}, "Net gains (losses) on cash flow hedging derivatives:(1) -- Net of tax": {"2019": 1.1, "2018": 0.2, "2017": -1.6, "Location of Amount Reclassified from AOCL": ""}, "Net gains (losses) on cash flow hedging derivatives:(1) -- Total reclassifications for the period": {"2019": -2.5, "2018": -1.9, "2017": -7.8, "Location of Amount Reclassified from AOCL": ""}}
prior_service_credits_2019 = df["Defined benefit pension plans and other post-employment benefits: -- Prior service credits"]["2019"]
prior_service_credits_2018 = df["Defined benefit pension plans and other post-employment benefits: -- Prior service credits"]["2018"]
prior_service_credits_2017 = df["Defined benefit pension plans and other post-employment benefits: -- Prior service credits"]["2017"]
answer = prior_service_credits_2019 + prior_service_credits_2018 + prior_service_credits_2017