A rope is cut from the middle each time and a section is taken away, so that after cutting 3 times, there is still 0.5 meters left. How long is this rope?
一根绳子每次从中间剪断后取走一段，这样剪了3次后还剩0.5米．这根绳子原来长多少米？
<gadget id="calculator">0.5 * 2 * 2 * 2</gadget>
<output>4</output>

<result>4</result>