students want to have a table tennis match, every 2 people play a ball. How many games will be played in total.
4个同学要进行一场乒乓球比赛，每2个人打一场球．一共要打多少场．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<result>6</result>