4 children, every two people talk on the phone once, how many times did they talk in total?
4位小朋友，每两人通一次电话，一共通了多少次话．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<result>6</result>