3-story building caught fire, and a firefighter took a ladder and climbed up to the 3-story building to rescue things. When he climbed to the middle step of the ladder, the window on the second floor spewed out fire, and he retreated 3 steps down. When the fire passed, he climbed up to level 7 again. At this time, a brick fell from the roof, and he stepped back 2 levels. Fortunately, the brick did not hit him, and he climbed 6 levels. At this time, he is still 3 levels away from the highest level. Think about it, how many steps there are in this ladder.
有一座3层的楼房着火了，一个救火队员搭了梯子爬到3层楼上去抢救东西．当他爬到梯子正中一级时，2楼的窗口喷出火来，他就往下退了3级．等到火过去了，他又爬上了7级．这时，屋顶上有一块砖头掉下来了，他又往后退了2级，幸亏砖头没有砸着他，他又爬了6级．这时他距离最高一级还有3级．你想想看，这梯子一共有多少级．
<gadget id="calculator">1 - 3 - 2</gadget>
<output>-4</output>

<gadget id="calculator">7 + 6 + 3 + (-4)</gadget>
<output>12</output>

<gadget id="calculator">2 - 1</gadget>
<output>1</output>

<gadget id="calculator">12 / 1</gadget>
<output>12</output>

<gadget id="calculator">12 * 2</gadget>
<output>24</output>

<gadget id="calculator">24 - 1</gadget>
<output>23</output>

<result>23</result>