Four classes in the third grade hold a tug-of-war competition, and there will be a game between every two classes. How many games will there be in total?
三年级4个班举行拔河比赛，每两个班之间要赛一场，一共要赛多少场．
<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>