In the fourth grade, 6 classes use the knockout system (that is, every two classes have to play one game) to play basketball games. How many games will be played in total?
在四年级6个班级采用淘汰赛制(即每两个班都要赛一场)进行篮球比赛，一共要进行多少场比赛．
<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">2 / 2</gadget>
<output>1</output>

<gadget id="calculator">3 + 1 + 1</gadget>
<output>5</output>

<result>5</result>