10 good friends meet at a party and shake hands once, how many times will they shake hands in total?
10个好朋友在一次聚会上见面，相互握手一次，一共要握手多少次．
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">9 * 5</gadget>
<output>45</output>

<result>45</result>