There are 6 players participating in a table tennis match. The rules of the game are a round robin match (one match between each two players). How many games are there in total?
一次乒乓球赛，共有6位选手参加，比赛规则采用循环赛(每两人之间都要赛一场)，共要赛多少场．
<gadget id="calculator">6 - 1</gadget>
<output>5</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">6 * (5/2)</gadget>
<output>15</output>

<result>15</result>