All the students of the aircraft model group stand in a row, the first, fifth, ninth... from left to right are female students, and the first, eighth, 15th from right to left... are male students. So, what is the maximum number of students in the model airplane group?
航模小组的所有同学站成一行，从左往右第1位、第5位、第9位…是女同学，从右往左第1位、第8位、第15位…是男同学．那么，航模小组最多有多少位同学．
<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<gadget id="calculator">16 + 1 + 1</gadget>
<output>18</output>

<result>18</result>