The youngest pupils in a certain school are 6 years old and the oldest are 13 years old. At least how many students are selected from this school will ensure that two of them are of the same age.
某校的小学生年龄最小的6岁，最大的13岁，从这个学校中至少任选多少位同学就一定保证其中有两位同学的年龄相同．
<gadget id="calculator">13 - 6</gadget>
<output>7</output>

<gadget id="calculator">7 + 1</gadget>
<output>8</output>

<gadget id="calculator">8 + 1</gadget>
<output>9</output>

<result>9</result>