function withdrawBack() public 
    {
        require(state == State.Disabled);

        uint256 tokens = investors[msg.sender];
        uint256 value = div( tokens, etherPrice );

        if (value > 0) 
        {
            investors[msg.sender] = 0;
            require( msg.sender.call.gas(gasPrice).value(value)() );

            totalSupply = sub( totalSupply, tokens );
        }
    }