There are 16 students in a competition, every two students shake hands once, how many times should they shake hands in total.
有16名同学比赛，每两名同学握一次手，一共要握多少次．
<gadget id="calculator">16 - 1</gadget>
<output>15</output>

<gadget id="calculator">16 / 2</gadget>
<output>8</output>

<gadget id="calculator">15 * 8</gadget>
<output>120</output>

<result>120</result>