The school holds a tug-of-war competition. There are 4 classes in the fourth grade. If there is a competition between every two classes, how many games will there be in total?
学校举行拔河比赛，四年级共有4个班，如果每两个班之间要进行一场比赛，那么一共要进行多少场比赛．
<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>