How much do the top 3 assets add up to in 2018?
{"Deferred compensation plan assets": {"2019": 6413, "2018": 5641}, "Investment in international licensees": {"2019": 2263, "2018": 2349}, "Equity investment in and loan to ThinxNet GmbH": {"2019": 2650, "2018": 2674}, "Equity investment in and loan to Smart Driver Club": {"2019": "-", "2018": 3814}, "Deferred product cost": {"2019": 10094, "2018": 3523}, "Other": {"2019": 1090, "2018": 828}, "": {"2019": 22510, "2018": 18829}}
top_3_assets_2018 = df["Deferred compensation plan assets"]["2018"] + df["Equity investment in and loan to Smart Driver Club"]["2018"] + df["Deferred product cost"]["2018"]
answer = top_3_assets_2018