3 people, every 2 people shake hands once, how many times did they shake hands in total?
3个人，每2人握一次手，一共握了多少次手．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">3 / 2</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">2 * (3/2)</gadget>
<output>3</output>

<result>3</result>