What is the change in value of frozen chicken between fiscal year 2019 and 2018?
{"Fresh, vacuum-sealed chicken": {"Fiscal Year 2019": 1310.2, "Fiscal Year 2018 ": 1139.3, "Fiscal Year 2017": 1339.1}, "Fresh, chill-packed chicken": {"Fiscal Year 2019": 1137.7, "Fiscal Year 2018 ": 1158.3, "Fiscal Year 2017": 1044.7}, "Fresh, ice-packed chicken ": {"Fiscal Year 2019": 511.5, "Fiscal Year 2018 ": 503.6, "Fiscal Year 2017": 547.1}, "Prepared chicken ": {"Fiscal Year 2019": 240.8, "Fiscal Year 2018 ": 207.6, "Fiscal Year 2017": 170.8}, "Frozen chicken ": {"Fiscal Year 2019": 213.0, "Fiscal Year 2018 ": 211.5, "Fiscal Year 2017": 223.9}, "Other ": {"Fiscal Year 2019": 27.1, "Fiscal Year 2018 ": 15.7, "Fiscal Year 2017": 16.6}, "Total net sales ": {"Fiscal Year 2019": 3440.3, "Fiscal Year 2018 ": 3236.0, "Fiscal Year 2017": 3342.2}}
frozen_chicken_fiscal_year_2019 = df["Frozen chicken "]["Fiscal Year 2019"]
frozen_chicken_fiscal_year_2018 = df["Frozen chicken "]["Fiscal Year 2018 "]
answer = frozen_chicken_fiscal_year_2019 - frozen_chicken_fiscal_year_2018