What is the percentage of research, development, and other related costs as well as litigation expenses over total operating expenses in 2018?
{"Revenue: -- Royalty and license fees": {"2019": 81943, "2018": 186425, "2017": 205809}, "Revenue: -- Total revenue": {"2019": 81943, "2018": 186425, "2017": 205809}, "Operating expenses: -- Research, development and other related costs": {"2019": 28732, "2018": 27514, "2017": 30039}, "Operating expenses: -- Litigation": {"2019": 3471, "2018": 26099, "2017": 36209}, "Operating expenses: -- Amortization": {"2019": 11871, "2018": 19906, "2017": 21590}, "Operating expenses: -- Total operating expenses (1)": {"2019": 44074, "2018": 73519, "2017": 87838}, "Operating expenses: -- Total operating income": {"2019": 37869, "2018": 112906, "2017": 117971}}
research_development_2018 = df["Operating expenses: -- Research, development and other related costs"]["2018"]
litigation_2018 = df["Operating expenses: -- Litigation"]["2018"]
total_operating_expenses_2018 = df["Operating expenses: -- Total operating expenses (1)"]["2018"]
answer = ( research_development_2018 + litigation_2018 ) / total_operating_expenses_2018 * 100.0