function setBonusRates(
    uint256[] _bonusDates,
    uint256[] _bonusRates
  )
    external
    onlyOwner
  {
    require(
      !started(),
      "Bonus rates can be set only before the campaign start"
    );
    require(
      _bonusDates.length == 4,
      "Dates array must have 4 entries."
    );
    require(
      _bonusRates.length == 4,
      "Rates array must have 4 entries."
    );
    require(
      _bonusDates[0] < _bonusDates[1] && _bonusDates[1] < _bonusDates[2] && _bonusDates[2] < _bonusDates[3], 
      "Dates must be consecutive"
    );

    bonusDates = _bonusDates;
    bonusRates = _bonusRates;
  }