15. The students in the military training perform in a queue and form a square team of 10 rows and 10 columns. Due to the limited space, it is necessary to remove a row and a column, and how much to remove.
15．军训的学生进行队列表演，排成了一个10行10列的方队，由于场地有限，需去掉一行一列，要去掉多少．
<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<gadget id="calculator">20 - 1</gadget>
<output>19</output>

<result>19</result>