$($d$)$ In the long$-$term debt structure of Ayayai Inc., the following three bonds were reported: mortgage bonds payable $$10,000,000$; collateral trust bonds $$5,016,000$; bonds maturing in installments, secured by plant equipment $$3,996,000.$

Determine the total amount, if any, of debenture bonds outstanding. $($Do not leave any answer field blank. Enter $0$ for amounts.$)$

Total amount $ $$