Ding Ding and the other 4 people in the group have an "arm wrestling" competition. If they have to compete once between two people, how many games will they have in total?
小丁丁和组内其余4人进行"扳手腕"比赛，如果他们每两个人间都要比赛一次，他们之间共要进行多少场比赛．
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<result>10</result>