For every 2 people playing a game of chess, how many games of chess should 5 people play in total?
每2人下一盘象棋，5个人一共要下多少盘象棋．
<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>