4 students have a table tennis match, every 2 people have a game, each person has to play. how many games
4名同学进行乒乓球比赛，每2人之间要比赛一场，每人要比赛．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>