A, B, and C go to the same copier to copy materials at the same time. A takes 3 minutes, B takes 6 minutes, and C takes 1 minute. According to the optimal arrangement, what is the minimum total time spent by the three of them?
甲、乙、丙三人同时到同一台复印机复印材料，甲要3分钟，乙要6分钟，丙要1分钟，按照最优方案安排，他们三人所花的总时间至少是多少？
<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<gadget id="calculator">1 + 3 + 6</gadget>
<output>10</output>

<gadget id="calculator">1 + 4 + 10</gadget>
<output>15</output>

<result>15</result>