A and B compete to climb stairs. When A reaches the 4th floor, B happens to reach the 3rd floor. The number of steps on each floor is the same. According to this calculation, when A reaches the 16th floor, how many floors does B reach?
甲乙二人比赛爬楼梯，甲跑到4层时，乙恰好跑到3层，每层楼的级数相同，照这样计算，甲跑到16层时，乙跑到多少层．
<gadget id="calculator">16 - 1</gadget>
<output>15</output>

<gadget id="calculator">15 / 3</gadget>
<output>5</output>

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

<gadget id="calculator">10 + 1</gadget>
<output>11</output>

<result>11</result>