If two people meet each other, they should shake hands once. According to this rule, how many times will 5 people shake hands in total when they meet each other?
两人见面都要握手一次，照这样规定5人见面共互相握手多少次．
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">4 * (5/2)</gadget>
<output>10</output>

<result>10</result>