There are 8 class reunions, every two people shake hands once, how many times do they shake hands in total?
8个同学聚会，每两个人要握一次手，一共要握多少次手？
<gadget id="calculator">8 - 1</gadget>
<output>7</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">7 * 4</gadget>
<output>28</output>

<result>28</result>