The oldest student in Yucai Primary School is 12 years old, and the youngest is 6 years old. At least how many students need to be selected from among them, so that two of the selected students must be of the same age.
育才小学学生的年龄最大是12岁，最小是6岁，至少需要从中挑选多少个同学，就一定能使挑出的同学中有两个的岁数相同．
<gadget id="calculator">12 - 6</gadget>
<output>6</output>

<gadget id="calculator">6 + 1 + 1</gadget>
<output>8</output>

<result>8</result>