When 3 children meet, every 2 children shake hands once, how many times do they shake hands in total?
3个小朋友见面，每2个小朋友握一次手，他们共握多少次手．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">2 / 2</gadget>
<output>1</output>

<gadget id="calculator">3 * 1</gadget>
<output>3</output>

<result>3</result>