What is the change in Contract liabilities: Current from 31 March 2019 to 1 April 2018?
{"": {"31 March 2019": "\u00a3m", "1 April 2018": "\u00a3m"}, "Contract assets -- Current": {"31 March 2019": 1353, "1 April 2018": 1417}, "Contract assets -- Non-current": {"31 March 2019": 249, "1 April 2018": 198}, "Contract assets -- ": {"31 March 2019": 1602, "1 April 2018": 1615}, "Contract liabilities -- Current": {"31 March 2019": 1225, "1 April 2018": 1406}, "Contract liabilities -- Non-current": {"31 March 2019": 200, "1 April 2018": 87}, "Contract liabilities -- ": {"31 March 2019": 1425, "1 April 2018": 1493}}
contract_liabilities_current_31_march_2019 = df["Contract liabilities -- Current"]["31 March 2019"]
contract_liabilities_current_1_april_2018 = df["Contract liabilities -- Current"]["1 April 2018"]
answer = contract_liabilities_current_31_march_2019 - contract_liabilities_current_1_april_2018