There is a 28-story high-rise building, there are 18 stairs between every two floors of this building, Zhang Xin lives in this building, he has to walk all the stairs (7/9) to his home, then, How many floors must Zhang Xin live in?
有一幢28层的高楼，这幢楼的每两层之间有18级楼梯，张欣住在这幢楼内，他到自己的家要走全部楼梯级数的(7/9)，那么，张欣一定住在多少层楼．
<gadget id="calculator">28 - 1</gadget>
<output>27</output>

<gadget id="calculator">7 / 9</gadget>
<output>7/9 = around 0.777778</output>

<gadget id="calculator">27 * (7/9)</gadget>
<output>21</output>

<gadget id="calculator">21 + 1</gadget>
<output>22</output>

<result>22</result>