Two people should shake hands once when they meet. According to this rule, how many times do five people shake hands when they meet?
两人见面要握一次手，照这样规定，5人见面握多少次手．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

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

<result>10</result>