In a sports competition, there are 5 players in total. If every two players shake hands once, how many times will they shake hands in total?
一场体育比赛中，一共有5名运动员，如果每两人握一次手，一共要握多少次手．
<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>