What is the percentage of altium designer software licenses in total product revenue in 2018?
{"Product Revenue": {"2019": 0, "2018": 0, "Change": "%"}, "Altium Designer software licenses": {"2019": 62377, "2018": 51309, "Change": 22}, "Altium Designer subscriptions": {"2019": 58468, "2018": 51522, "Change": 13}, "Octopart search advertising": {"2019": 17940, "2018": 11968, "Change": 50}, "TASKING software licenses": {"2019": 12293, "2018": 8526, "Change": 44}, "TASKING maintenance": {"2019": 5741, "2018": 4709, "Change": 22}, "Altium Nexus": {"2019": 6635, "2018": 4848, "Change": 37}, "Service revenue": {"2019": 3655, "2018": 4833, "Change": -25}, "Other": {"2019": 4710, "2018": 2461, "Change": 91}, "Total Product Revenue": {"2019": 171819, "2018": 140176, "Change": 23}}
altium_designer_licenses_2018 = df["Altium Designer software licenses"]["2018"]
total_product_revenue_2018 = df["Total Product Revenue"]["2018"]
answer = altium_designer_licenses_2018 / total_product_revenue_2018 * 100.0