There are 30 students, every two students shake hands once, how many times should they shake hands in total?
有30位同学，每两位同学握一次手，一共要握几次手？
<gadget id="calculator">30 - 1</gadget>
<output>29</output>

<gadget id="calculator">29 / 2</gadget>
<output>29/2 = around 14.5</output>

<gadget id="calculator">30 * (29/2)</gadget>
<output>435</output>

<result>435</result>