What is the percentage constitution of trade names among the total intangible assets subject to amortization?
{"": {"Fair Value": "(U.S. $ in thousands)", "Useful Life": "(years)"}, "Developed technology": {"Fair Value": 50600, "Useful Life": 3}, "Customer relationships": {"Fair Value": 56900, "Useful Life": 2}, "Trade names": {"Fair Value": 19900, "Useful Life": 3}, "Total intangible assets subject to amortization": {"Fair Value": 127400, "Useful Life": ""}}
trade_names_fair_value = df["Trade names"]["Fair Value"]
total_intangible_assets_subject_to_amortization_fair_value = df["Total intangible assets subject to amortization"]["Fair Value"]
answer = trade_names_fair_value / total_intangible_assets_subject_to_amortization_fair_value * 100.0