There are 27 seats in a row of chairs. For the convenience of those who come later, there will be people next to him in any position, so at least how many people should be seated first.
有一排椅子有27个座位，为了方便后去的人随意坐在哪个位置都有人与他相邻，则至少要先坐多少人．
<gadget id="calculator">27 / 3</gadget>
<output>9</output>

<result>9</result>