What was the change in Revenue deferred and acquired in current period between 2018 and 2019?
{"Year Ended December 31, -- ": {"2019": 2019, "2018": 2018}, "Year Ended December 31, -- Beginning of period balance": {"2019": 11176, "2018": 12678}, "Year Ended December 31, -- Revenue deferred and acquired in current period": {"2019": 6127, "2018": 3954}, "Year Ended December 31, -- Revenue recognized from amounts included in contract liabilities": {"2019": -6805, "2018": -5456}, "Year Ended December 31, -- End of period balance": {"2019": 10498, "2018": 11176}}
revenue_2019 = df["Year Ended December 31, -- Revenue deferred and acquired in current period"]["2019"]
revenue_2018 = df["Year Ended December 31, -- Revenue deferred and acquired in current period"]["2018"]
answer = revenue_2019 - revenue_2018