What was the sum of amortized cost of corporate bonds and US treasury securities?
{"Current assets: -- Cash": {"Amortized Cost": 54275, "Unrealized Gains": "$\u2014", "Unrealized Losses": "$\u2014", "Fair Value": 54275}, "Cash equivalents: -- Money market funds": {"Amortized Cost": 129321, "Unrealized Gains": "\u2014", "Unrealized Losses": "\u2014", "Fair Value": 129321}, "Cash equivalents: -- Total cash equivalents": {"Amortized Cost": 129321, "Unrealized Gains": "\u2014", "Unrealized Losses": "\u2014", "Fair Value": 129321}, "Cash equivalents: -- Total cash and cash equivalents": {"Amortized Cost": 183596, "Unrealized Gains": "\u2014", "Unrealized Losses": "\u2014", "Fair Value": 183596}, "Short-term investments: -- Corporate bonds": {"Amortized Cost": 58115, "Unrealized Gains": "\u2014", "Unrealized Losses": -82, "Fair Value": 58033}, "Short-term investments: -- US treasury securities": {"Amortized Cost": 138826, "Unrealized Gains": "\u2014", "Unrealized Losses": -100, "Fair Value": 138726}, "Short-term investments: -- Commercial paper": {"Amortized Cost": 7973, "Unrealized Gains": "\u2014", "Unrealized Losses": "\u2014", "Fair Value": 7973}, "Short-term investments: -- Total short-term investments": {"Amortized Cost": 204914, "Unrealized Gains": "\u2014", "Unrealized Losses": -182, "Fair Value": 204732}, "Long-term investments: -- Strategic investments": {"Amortized Cost": 1250, "Unrealized Gains": "\u2014", "Unrealized Losses": "\u2014", "Fair Value": 1250}, "Long-term investments: -- Total long-term investments": {"Amortized Cost": 1250, "Unrealized Gains": "$\u2014", "Unrealized Losses": "$\u2014", "Fair Value": 1250}}
corporate_bonds_amortized_cost = df["Short-term investments: -- Corporate bonds"]["Amortized Cost"]
us_treasury_securities_amortized_cost = df["Short-term investments: -- US treasury securities"]["Amortized Cost"]
answer = corporate_bonds_amortized_cost + us_treasury_securities_amortized_cost