What is the change in the value of total assets between 2019 and 2018?
{"": {"2019": "", "2018": "", "2017": "(In thousands)", "2016": "", "2015": ""}, "Cash and cash equivalents": {"2019": 19505, "2018": 18017, "2017": 22553, "2016": 26838, "2015": 35128}, "Working capital": {"2019": 1116, "2018": 6356, "2017": 7646, "2016": 14643, "2015": 16046}, "Total assets": {"2019": 54538, "2018": 43424, "2017": 45672, "2016": 53530, "2015": 68579}, "Stockholders' equity": {"2019": 10863, "2018": 14059, "2017": 13078, "2016": 18064, "2015": 21387}}
total_assets_2019 = df["Total assets"]["2019"]
total_assets_2018 = df["Total assets"]["2018"]
answer = total_assets_2019 - total_assets_2018