Mom bought some eggs and ate half and half of them on the first day, the remaining half and half on the second day, and half and half of the rest on the third day. At this time, there is still 1 egg left. How many eggs did mother buy back in total?
妈妈买回来一些鸡蛋，第一天吃了全部的一半又半个，第二天吃了余下的一半又半个，第三天吃了第二天余下的一半又半个．这时还剩下1个鸡蛋，妈妈一共买回多少个鸡蛋？
<gadget id="calculator">1 + 0.5</gadget>
<output>1.5</output>

<gadget id="calculator">2 * 1.5</gadget>
<output>3</output>

<gadget id="calculator">3 + 0.5</gadget>
<output>3.5</output>

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

<gadget id="calculator">7 + 0.5</gadget>
<output>7.5</output>

<gadget id="calculator">2 * 7.5</gadget>
<output>15</output>

<result>15</result>