On the podium of a mathematics competition, 5 students came to the stage to accept the prize, and each of them shook hands with each other once. Ask them how many times they shook hands.
在一次数学竞赛的领奖台上，有5名同学上台领奖，他们每两人都相互握了一次手．问他们共握了多少次手．
<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>