What is the sum of Three-year PSU awards for all years as of 2019?
{"2019 Three-year PSU Awards": {"2019": 4.3, "2018": "$ \u2014", "2017": "$ \u2014"}, "2018 Three-year PSU Awards": {"2019": 0.2, "2018": 2.7, "2017": "\u2014"}, "2017 Three-year PSU Awards(1)": {"2019": "\u2014", "2018": 3.7, "2017": 9.8}, "2017 COO and Chief Executive Officer-Designate 2017 New Hire Equity Awards": {"2019": 0.2, "2018": 0.2, "2017": 0.1}, "2016 Three-year PSU Awards(1)": {"2019": "\u2014", "2018": -3.0, "2017": 2.0}, "2016 President & CEO Inducement Award": {"2019": "\u2014", "2018": "\u2014", "2017": 0.5}, "2015 Three-year PSU Awards": {"2019": "\u2014", "2018": "\u2014", "2017": -0.8}, "2014 Special PSU Awards(2)": {"2019": "\u2014", "2018": "\u2014", "2017": 3.2}, "SLO Awards": {"2019": 3.2, "2018": 1.6, "2017": 1.1}, "Other long-term share-based incentive compensation programs(3)(4)": {"2019": 26.5, "2018": 24.7, "2017": 32.6}, "Total share-based incentive compensation expense(5)": {"2019": 34.4, "2018": 29.9, "2017": 48.5}, "Associated tax benefits recognized": {"2019": 5.8, "2018": 4.9, "2017": 11.8}}
three_year_psu_2019 = df["2019 Three-year PSU Awards"]["2019"]
three_year_psu_2018 = df["2018 Three-year PSU Awards"]["2019"]
answer = three_year_psu_2019 + three_year_psu_2018