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LONG-TERM INCENTIVE PLANS - Stock option activity (Details) | 12 Months Ended
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Dec. 31, 2017 BRL (R$) Options shares | Dec. 31, 2016 BRL (R$) Options | Dec. 31, 2015 BRL (R$) Options
Preferred shares |  |  |
Average exercise price in the year |  |  |
Treasury shares | shares | 8,704,061 |  |
Stock options |  |  |
Number of shares |  |  |
Balance, beginning of year | Options | 569,115 | 1,074,246 | 2,448,973
Options Exercised | Options |  |  | (25,210)
Options Forfeited | Options | (276,724) | (505,131) | (1,349,517)
Balance, end of year | Options | 292,391 | 569,115 | 1,074,246
Average exercise price in the year |  |  |
Beginning of year | R$ 16.64 | R$ 18.36 | R$ 19.53
Options Exercised |  |  | 19.56
Options Forfeited | 15.11 | 20.49 | 20.98
End of year | 17.91 | 16.64 | 18.36
Average market price of the share | R$ 11.19 | R$ 7.68 | R$ 7.70

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