What is the difference in the total debt investments and the total equity investments, based on amortized cost?
{"Marketable debt securities -- U.S. treasury securities": {"Amortized Cost": 101563, "Unrealized Gains": 203, "Unrealized Losses": -7, "Fair Value": 101759}, "Marketable debt securities -- Agency securities": {"Amortized Cost": 26936, "Unrealized Gains": 33, "Unrealized Losses": -3, "Fair Value": 26966}, "Marketable debt securities -- Certificates of deposit and time deposits": {"Amortized Cost": 24126, "Unrealized Gains": "\u2014", "Unrealized Losses": "\u2014", "Fair Value": 24126}, "Marketable debt securities -- Commercial paper": {"Amortized Cost": 94035, "Unrealized Gains": "\u2014", "Unrealized Losses": "\u2014", "Fair Value": 94035}, "Marketable debt securities -- Corporate debt securities": {"Amortized Cost": 201552, "Unrealized Gains": 292, "Unrealized Losses": -24, "Fair Value": 201820}, "Marketable debt securities -- Total debt investments": {"Amortized Cost": 448212, "Unrealized Gains": 528, "Unrealized Losses": -34, "Fair Value": 448706}, "Equity Investments -- Marketable equity securities": {"Amortized Cost": 20270, "Unrealized Gains": 38662, "Unrealized Losses": "\u2014", "Fair Value": 58932}, "Equity Investments -- Non-marketable equity securities": {"Amortized Cost": 3000, "Unrealized Gains": "\u2014", "Unrealized Losses": "\u2014", "Fair Value": 3000}, "Equity Investments -- Total equity investments": {"Amortized Cost": 23270, "Unrealized Gains": 38662, "Unrealized Losses": "\u2014", "Fair Value": 61932}, "Equity Investments -- Total investments": {"Amortized Cost": 471482, "Unrealized Gains": 39190, "Unrealized Losses": -34, "Fair Value": 510638}}
total_debt_investments = df["Marketable debt securities -- Total debt investments"]["Amortized Cost"]
total_equity_investments = df["Equity Investments -- Total equity investments"]["Amortized Cost"]
answer = total_debt_investments - total_equity_investments