A pencil uses half of it first, and then uses the remaining half. At this time, it is still 4 centimeters long. How long is this pencil in centimeters?
一支铅笔先用去它的一半，再用去剩下的一半，这时还长4厘米，原来这支铅笔长多少厘米？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">4 / (1/2) / (1/2)</gadget>
<output>16</output>

<result>16</result>