piece of iron wire, half of which is used for the first time is less than 1 meter, the remaining half is used for the second time and the remaining half is more than 1 meter, and finally 2.5 meters are left. What is the original length of the iron wire?
一条铁丝，第一次用去它的一半少1米，第二次用去了余下的一半多1米，最后剩2.5米，铁丝原来长多少米．
<gadget id="calculator">2.5 + 1</gadget>
<output>3.5</output>

<gadget id="calculator">3.5 * 2</gadget>
<output>7</output>

<gadget id="calculator">7 - 1</gadget>
<output>6</output>

<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<result>12</result>