16 children are arranged in a row, and the distance between every two children is 2 meters. What is the distance between the first child and the last one?
16个小朋友排成一行，每两个小朋友之间间隔2米，第一个小朋友和最后一个相距多少米．
<gadget id="calculator">16 - 1</gadget>
<output>15</output>

<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<result>30</result>