Xiao Shan attended a Xinhui summer camp with 12 people. When parting, every two people shook hands once. How many times did they shake hands in total?
小山出席一个有12人组成的新会夏令营活动，离别时每两人相互握一次手，他们一共握手多少次．
<gadget id="calculator">12 - 1</gadget>
<output>11</output>

<gadget id="calculator">11 / 2</gadget>
<output>11/2 = around 5.5</output>

<gadget id="calculator">12 * (11/2)</gadget>
<output>66</output>

<result>66</result>