Three customers go to the same counter to buy things. A needs 4 minutes, B needs 6 minutes, and C needs 2 minutes. How to arrange their purchase sequence so that the total time they spend is the least? How many minutes is the minimum?
三个顾客到同一个柜台去买东西，甲需要用4分钟，乙需要用6分钟，丙需要用2分钟．怎样安排他们的购买顺序，使他们所花的总时间最少？最少是多少分钟？
<gadget id="calculator">2 * 3</gadget>
<output>6</output>

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

<gadget id="calculator">6 + 8 + 6</gadget>
<output>20</output>

<result>20</result>