The youngest student in Taishi Elementary School is 7 years old and the oldest is 13 years old. If you choose as many students as you want from this school, you will be sure that two of them are of the same age.
台实小的学生年龄最小7岁，最大13岁，从这个学校中任选多少个同学，就一定能保证其中有两位同学的年龄相同．
<gadget id="calculator">13 - 7</gadget>
<output>6</output>

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

<result>8</result>