What is the difference in minimum rentals between 2018 and 2019?
{"Minimum rentals": {"2019": 184587, "2018": 184106, "2017": 185696}, "Contingent rentals": {"2019": 2255, "2018": 2221, "2017": 2419}, "Total rent expense": {"2019": 186842, "2018": 186327, "2017": 188115}, "Less rental expense on subleased properties": {"2019": -170651, "2018": -162640, "2017": -145728}, "Net rent expense": {"2019": 16191, "2018": 23687, "2017": 42387}}
minimum_rentals_2019 = df["Minimum rentals"]["2019"]
minimum_rentals_2018 = df["Minimum rentals"]["2018"]
answer = minimum_rentals_2019 - minimum_rentals_2018