There were 5 classmates among the graduates of class 6 and 1 who had a reunion. They all shook hands once. How many times did you shake hands in this reunion?
六1班毕业生中有5名同学聚会了，他们互相都握了一次手，这次聚会大家一共握了多少次手．
<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>