A, B, C, and D take buckets to lift water. The time required for them to fill the bucket is 4 minutes, 3 minutes, 5 minutes, and 2 minutes respectively. Now there is only one faucet available, what is the sum of the minimum waiting time for the four of them to receive water?
甲、乙、丙、丁四人拿桶去提水，他们接满桶的所需时间分别是4分、3分、5分、2分．现只有一个水龙头可用，他们四人接水的最少等候时间的总和是多少分钟．
<gadget id="calculator">2 * 4</gadget>
<output>8</output>

<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">8 + 9 + 8 + 5</gadget>
<output>30</output>

<result>30</result>