The production of the "New Hope Cup" crystal trophy requires a total of five processes A, B, C, D, and E. Process A requires 5 hours, process B requires 6 hours, process C requires 8 hours, process D requires 2 hours, and process E requires 7 hours. Some processes can be carried out at the same time, but processes B and C must be carried out after process A is completed; processes D and E must be carried out after process B is completed. What is the minimum hours required to produce this trophy
制作"新希望杯"水晶奖杯共需A、B、C、D、E五道工序，A工序需要5小时、B工序需要6小时、C工序需要8小时、D工序需要2小时、E工序需要7小时．有些工序可同时进行，但工序B、C必须在工序A完成之后才能进行；工序D、E必须在工序B完成之后才能进行．那么生产这种奖杯最少需多少小时
<gadget id="calculator">8 - 2</gadget>
<output>6</output>

<gadget id="calculator">5 + 6 + 7</gadget>
<output>18</output>

<result>18</result>