Three children skip rope in a competition. Every 2 children compete once, how many times in total.
三个小朋友比赛跳绳，每2个小朋友比一次，一共要比多少次．
<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>