12 girls are lined up in a line, and a boy is inserted between every 2 girls, how many boys can be inserted in total.
12名女生排成一队，每2名女生之间插进1名男生，一共可以插进多少名男生．
<gadget id="calculator">12 - 1</gadget>
<output>11</output>

<result>11</result>