It is stipulated that every two people meet to shake hands once, how many times should five people meet?
规定每两个人见面要握手一次，5人见面要握手几次？
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<result>10</result>