function startCrowdsale(uint256 timestamp) internal {
        startDate = timestamp;

        
        firstBonusSalesEnds = startDate + 7 days;             
        secondBonusSalesEnds = firstBonusSalesEnds + 14 days; 
        thirdBonusSalesEnds = secondBonusSalesEnds + 14 days; 
        fourthBonusSalesEnds = thirdBonusSalesEnds + 7 days;  
        fifthBonusSalesEnds = fourthBonusSalesEnds + 3 days;  

        
        firstExtendedBonusSalesEnds = fifthBonusSalesEnds + 3 days;         
        secondExtendedBonusSalesEnds = firstExtendedBonusSalesEnds + 3 days; 
        thirdExtendedBonusSalesEnds = secondExtendedBonusSalesEnds + 3 days; 
        fourthExtendedBonusSalesEnds = thirdExtendedBonusSalesEnds + 3 days; 
        fifthExtendedBonusSalesEnds = fourthExtendedBonusSalesEnds + 3 days;  
        sixthExtendedBonusSalesEnds = fifthExtendedBonusSalesEnds + 60 days; 
    }