There are 8 people participating in a meeting. Every two people in the meeting should shake hands once. How many times should they shake hands in total?
一次会议有8个人参加，参会的人每两个人都要握一次手，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>