What was the change in the The audit of the parent company and the consolidated financial statements from 2018 to 2019?
{"Year ended 31 March": {"2019": 0, "2018": 0, "2017": 0}, "Audit services a,b -- The audit of the parent company and the consolidated financial statements": {"2019": 8165, "2018": 5418, "2017": 4316}, "Audit services a,b -- The audit of the companys subsidiaries": {"2019": 6061, "2018": 5877, "2017": 5675}, "Audit services a,b -- ": {"2019": 14226, "2018": 11295, "2017": 9991}, "Audit services a,b -- Audit related assurance services c": {"2019": 2236, "2018": 1771, "2017": 1865}, "Other non-audit services -- Taxation compliance services d": {"2019": "\u2013", "2018": "\u2013", "2017": 366}, "Other non-audit services -- Taxation advisory services e": {"2019": "\u2013", "2018": "\u2013", "2017": 111}, "Other non-audit services -- All other assurance services f": {"2019": 748, "2018": 211, "2017": 200}, "Other non-audit services -- All other services g": {"2019": 210, "2018": 592, "2017": 2332}, "Other non-audit services -- ": {"2019": 958, "2018": 803, "2017": 3009}, "Other non-audit services -- Total services": {"2019": 17420, "2018": 13869, "2017": 14865}}
audit_2019 = df["Audit services a,b -- The audit of the parent company and the consolidated financial statements"]["2019"]
audit_2018 = df["Audit services a,b -- The audit of the parent company and the consolidated financial statements"]["2018"]
answer = audit_2019 - audit_2018