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EQUITY - Treasury stocks (Details) - BRL (R$) R$ / shares in Units, R$ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Capital |  |  |
Number of shares outstanding at end of period | 1,696,164,000 |  |
Equity at beginning of period | R$ 23,893,941 | R$ 24,274,653 | R$ 31,970,383
Repurchases | 243,723 |  | 95,370
Exercise of stock options | 23,354 | 19,682 | 5,560
Transfer of shares | 18,984 |  | 205,800
Equity at end of period | R$ 25,938,571 | R$ 23,893,941 | R$ 24,274,653
Investments and working capital reserve |  |  |
Investments and working capital reserve, annual percentage | 5.00% |  |
Common shares |  |  |
Capital |  |  |
Number of shares outstanding at beginning of the year | 571,929,945 | 571,929,945 | 571,929,945
Number of shares outstanding at end of period | 571,929,945 | 571,929,945 | 571,929,945
Preferred shares |  |  |
Capital |  |  |
Number of shares outstanding at beginning of the year | 1,137,327,184 | 1,137,018,570 | 1,114,744,538
Repurchases | 16,000,000 |  | 10,000,000
Exercise of stock options | 1,597,235 | 308,614 | 2,274,032
Transfer of shares | 1,309,336 |  | 30,000,000
Number of shares outstanding at end of period | 1,124,233,755 | 1,137,327,184 | 1,137,018,570
Treasury Stocks |  |  |
Capital |  |  |
Equity at beginning of period | R$ (76,085) | R$ (98,746) | R$ (383,363)
Repurchases | 243,396 |  | 95,343
Exercise of stock options | 27,433 | 22,661 | 10,461
Transfer of shares | 11,622 |  | 369,499
Equity at end of period | R$ (280,426) | R$ (76,085) | R$ (98,746)
Average acquisition cost | R$ 12.84 | R$ 8.68 | R$ 10.89
Treasury Stocks | Common shares |  |  |
Capital |  |  |
Number of shares outstanding at beginning of the year | 1,697,538 | 1,697,538 | 1,697,538
Number of shares outstanding at end of period | 1,697,538 | 1,697,538 | 1,697,538
Equity at beginning of period | R$ 557 | R$ 557 | R$ 557
Equity at end of period | R$ 557 | R$ 557 | R$ 557
Treasury Stocks | Preferred shares |  |  |
Capital |  |  |
Number of shares outstanding at beginning of the year | 8,704,061 | 9,012,675 | 31,286,707
Repurchases | 16,000,000 |  | 10,000,000
Exercise of stock options | (1,597,235) | (308,614) | (2,274,032)
Transfer of shares | (1,309,336) |  | (30,000,000)
Number of shares outstanding at end of period | 21,797,490 | 8,704,061 | 9,012,675
Equity at beginning of period | R$ 75,528 | R$ 98,189 | R$ 382,806
Repurchases | 243,396 |  | 95,343
Exercise of stock options | (27,433) | (22,661) | (10,461)
Transfer of shares | (11,622) |  | (369,499)
Equity at end of period | R$ 279,869 | R$ 75,528 | R$ 98,189

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