There are several basketballs in the warehouse. The physical education teacher takes half of them each time and puts back a basketball. This is done 6 times in total. There are still 4 basketballs in the warehouse. How many basketballs are there in the warehouse?
仓库里有若干个篮球，体育老师每次拿走其中的一半，再放回一个篮球，这样一共做了6次，仓库里还有4个篮球，原来仓库里有多少个篮球？
<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>