What was the change in Research and Development between 2018 and 2019?
{"Cost of revenues": {"2019": 723, "2018": 653, "2017": 374}, "Research and development": {"2019": 2061, "2018": 1471, "2017": 1033}, "Selling and marketing": {"2019": 2863, "2018": 2314, "2017": 1655}, "General and administrative": {"2019": 5382, "2018": 4860, "2017": 4771}, "": {"2019": 11029, "2018": 9298, "2017": 7833}}
research_and_development_2019 = df["Research and development"]["2019"]
research_and_development_2018 = df["Research and development"]["2018"]
answer = research_and_development_2019 - research_and_development_2018