On Children's Day, a row of colorful flags hung at the school gate. Counting from the front, the red flag is the 8th for Xiao Zhang; counting from the back, the red flag is the 10th. How many sides are there in this row of colored flags?
六一儿童节，学校门口挂了一行彩旗．小张从前数起，红旗是第8面；从后数起，红旗是第10面．这行彩旗共多少面．
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<gadget id="calculator">8 + 9</gadget>
<output>17</output>

<result>17</result>