There are 20 volleyball teams, and every two teams will play a volleyball match. How many games will be played in total?
有20支排球队，每两支队要进行一场排球比赛，一共要进行多少场比赛？
<gadget id="calculator">20 - 1</gadget>
<output>19</output>

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">19 * 10</gadget>
<output>190</output>

<result>190</result>