6 players are playing table tennis, if every two players play a game, how many games will there be in total?
6名选手进行乒乓球比赛，如果每两人进行一场比赛，一共要赛多少场．
<gadget id="calculator">6 - 1</gadget>
<output>5</output>

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

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<result>15</result>