During the winter vacation, Xiao Ming and 4 classmates exchanged phone calls once, how many calls will they have to make in total?
寒假里，小明和4位同学互通一次电话，一共要通多少次电话．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<result>10</result>