function _depositTokens(address _beneficiary, uint256 _amountTokens) internal {
    require(_amountTokens != 0);

    if (investors[_beneficiary] == 0) {
      investorCount++;
    }

    investors[_beneficiary] = investors[_beneficiary].add(_amountTokens);

    mintableFida.sendBoughtTokens(_beneficiary, _amountTokens);
  }