What was the change in international assets between 2018 and 2019?
{"U.S.": {"April 26, 2019": 159, "April 27, 2018": 853}, "International": {"April 26, 2019": 3740, "April 27, 2018": 4538}, "Total": {"April 26, 2019": 3899, "April 27, 2018": 5391}}
international_2019 = df["International"]["April 26, 2019"]
international_2018 = df["International"]["April 27, 2018"]
answer = international_2019 - international_2018