bucket filled with a certain amount of water, we pour out half of its water, and then add one liter of water. Add another liter of water, if after 7 operations, there are still 3 liters of water in the bucket, then, how many liters of water is in the bucket.
一只装了若干水的水桶，我们把它的水倒出一半，然后再加入一升水，这算一次操作，第二次操作是把经过第一次操作的水桶里的水倒出一半，然后再加入一升水，如果经过7次操作后，桶里还有3升水，那么，这只水桶原来有水多少升．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">2 * 3</gadget>
<output>6</output>

<gadget id="calculator">6 - 1</gadget>
<output>5</output>

<gadget id="calculator">2 * 5</gadget>
<output>10</output>

<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<gadget id="calculator">2 * 9</gadget>
<output>18</output>

<gadget id="calculator">18 - 1</gadget>
<output>17</output>

<gadget id="calculator">2 * 17</gadget>
<output>34</output>

<gadget id="calculator">34 - 1</gadget>
<output>33</output>

<gadget id="calculator">2 * 33</gadget>
<output>66</output>

<gadget id="calculator">66 - 1</gadget>
<output>65</output>

<gadget id="calculator">2 * 65</gadget>
<output>130</output>

<result>130</result>