There are 27 seats in a row of chairs. At least how many people must be seated so that no matter which seat the person who goes after is sitting next to him.
有一排椅子共27个座位，至少要坐多少人，才能使后去的人无论坐在哪个座位都有人与他相邻．
<gadget id="calculator">27 / 3</gadget>
<output>9</output>

<result>9</result>