function approve(address _spender, uint256 _amount) public returns(bool success) {
        require((_amount == 0) || (allowance[msg.sender][_spender] == 0));
        
        if(now < (dayStart + 365 days)){
            require(msg.sender != foundersAddress && tx.origin != foundersAddress);
        }
        
        if(now < (dayStart + 180 days)){
            require(msg.sender != bonusAddress && tx.origin != bonusAddress);
        }
        
        
        allowance[msg.sender][_spender] = _amount;
        return true;
    }