Calculation of insurance benefits
Insurance benefits shall be paid in accordance with section 1735d of this title and shall be equal to the original principal obligation of the mortgage (with such additions and deductions as the Secretary determines are appropriate) which was unpaid upon the date of—
(A) assignment of the mortgage to the Secretary;
(B) the institution of foreclosure proceedings;
(C) the acquisition of the property after default other than by foreclosure; or
(D) sale of the mortgaged property by the mortgagor.