What was the change in CPI inflation percentage in 2019 from 2018?
{"": {"2019": "%", "2018": "%"}, "Discount rate for scheme liabilities": {"2019": 2.45, "2018": 2.6}, "CPI inflation": {"2019": 2.35, "2018": 2.25}, "RPI inflation": {"2019": 3.45, "2018": 3.35}, "Pension increases -- Pre 1988 GMP": {"2019": "\u2013", "2018": "\u2013"}, "Pension increases -- Post 1988 GMP": {"2019": 2.1, "2018": 2.1}, "Pension increases -- Pre 2004 non GMP": {"2019": 5.0, "2018": 5.0}, "Pension increases -- Post 2004": {"2019": 3.35, "2018": 3.25}}
cpi_inflation_2019 = df["CPI inflation"]["2019"]
cpi_inflation_2018 = df["CPI inflation"]["2018"]
answer = cpi_inflation_2019 - cpi_inflation_2018