For every 2 people making one phone call, how many times will the four people make a total of phone calls?
每2人通一次电话，四个人一共通多少次电话．
<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>