Students in two classes of fifth grade line up for exercise together. If 9 people line up, there will be one more person; if 10 people line up, there will also be one more person. What is the minimum number of people in these two classes?
五年级两个班的学生一起排队出操，如果9人排一行，多出一个人；如果10人排一行，同样多出一个人．这两个班最少共有多少人．
<gadget id="calculator">9 * 10</gadget>
<output>90</output>

<gadget id="calculator">90 + 1</gadget>
<output>91</output>

<result>91</result>