Losses sustained by a bank or trust company in excess of retained earnings may be charged to paid-in capital or to appropriated retained earnings, provided that a bank or trust company shall not pay any dividends so long as its paid-in capital and appropriated retained earnings do not, in combination, equal at least 20 percent of its capital stock. Earnings shall, not later than the end of each fiscal year, be transferred to appropriated retained earnings until such required 20 percent margin is obtained.