Donut Co. uses a periodic inventory system.  Beginning inventory on January 1 was understated by $30,000, and its ending inventory on December 31 was understated by $17,000.  In addition, a purchase of merchandise costing $20,000 was incorrectly recorded as a $2,000 purchase.  None of these errors were discovered until the next year.  As a result, Donut's cost of goods sold for this year was understated or overstated by $31,000?