S.D. Codified Laws § 21-49-26

The holder of the mortgage may purchase the premises or any part thereof at the foreclosure sale if the holder bids therefor the full amount of the judgment debt, less the sum of the balances due, as of the date of sale, on any prior liens or encumbrances upon the mortgaged premises, including liens or charges for real property taxes and special assessments. In no event, however, may the holder of the mortgage be required to bid a sum in excess of the debt adjudged to be due, with the costs included in the judgment upon which sale was made, and expenses of sale.