What was the percentage change in derivative financial instruments from 2018 to 2019?
{"Cash and cash equivalents": {"2018": 342594, "2019": 263747}, "Short-term investments": {"2018": 25000, "2019": 4500}, "Trade and other receivables": {"2018": 20244, "2019": 24900}, "Dividends receivable and other amounts due from related parties": {"2018": 33395, "2019": 573}, "Derivative financial instruments": {"2018": 15188, "2019": 4001}}
derivative_financial_instruments_2019 = df["Derivative financial instruments"]["2019"]
derivative_financial_instruments_2018 = df["Derivative financial instruments"]["2018"]
answer = (derivative_financial_instruments_2019 - derivative_financial_instruments_2018) / derivative_financial_instruments_2018 * 100.0