What is the change in Interest before impact of interest rate caps from Years Ended December 31, 2018 to 2019?
{"Interest before impact of interest rate caps": {"2019": 25633, "2018": 30709}, "Impact of interest rate caps": {"2019": "\u2014", "2018": 181}, "Interest expense": {"2019": 25633, "2018": 30890}}
interest_2019 = df["Interest before impact of interest rate caps"]["2019"]
interest_2018 = df["Interest before impact of interest rate caps"]["2018"]
answer = interest_2019 - interest_2018