Five players take part in a table tennis match. Every two students shake hands once before the match. How many times do they shake hands in total?
5名选手参加乒乓球比赛，比赛前每两名同学都要握一次手，他们一共要握手多少次．
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">4 * (5/2)</gadget>
<output>10</output>

<result>10</result>