4 children make a phone call every 2 people, how many times will they make a phone call in total?
4个小朋友每2个人通一次电话，一共要通多少次电话．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

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

<result>6</result>