The athletes of class 201 are arranged in 2 rows with equal numbers. Xiaoming is in the first row. He is the 6th from the front and the 4th from the back. How many athletes are there in class 201?
201班的运动员排成人数相等的2行，小明排在第一行，从前数他是第6个，从后数他是第4个，201班共有多少个运动员．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">6 + 3</gadget>
<output>9</output>

<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<result>18</result>