What is the percentage change in total revenue in 2019 compared to 2018?
{"Revenue: -- Royalty and license fees": {"2019": 198124, "2018": 219708, "2017": 167923}, "Revenue: -- Total revenue": {"2019": 198124, "2018": 219708, "2017": 167923}, "Operating expenses: -- Cost of revenues": {"2019": 8460, "2018": 13291, "2017": 6308}, "Operating expenses: -- Research, development and other related costs": {"2019": 83613, "2018": 78892, "2017": 75809}, "Operating expenses: -- Litigation": {"2019": 1656, "2018": "\u2014", "2017": 288}, "Operating expenses: -- Amortization": {"2019": 88075, "2018": 88544, "2017": 90340}, "Operating expenses: -- Total operating expenses (1)": {"2019": 181804, "2018": 180727, "2017": 172745}, "Operating expenses: -- Total operating income (loss)": {"2019": 16320, "2018": 38981, "2017": -4822}}
revenue_2019 = df["Revenue: -- Royalty and license fees"]["2019"]
revenue_2018 = df["Revenue: -- Royalty and license fees"]["2018"]
answer = (revenue_2019 - revenue_2018) / revenue_2018 * 100.0