A and B compete to climb the stairs. When A reaches the 5th floor, B happens to reach the 3rd floor. According to this calculation, when A runs to the 17th floor, how many floors does B go to?
甲、乙两人比赛爬楼梯，甲跑到5楼时，乙恰好跑到3楼．照这样计算，甲跑到17楼时，乙跑到多少层．
<gadget id="calculator">17 - 1</gadget>
<output>16</output>

<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">3 - 1</gadget>
<output>2</output>

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

<gadget id="calculator">16 / 2</gadget>
<output>8</output>

<gadget id="calculator">8 + 1</gadget>
<output>9</output>

<result>9</result>