10 little ducks stand in a row, and there is a big duck standing between every two little ducks. How many big ducks are there?
10只小鸭子站成一排，每两只小鸭子中间站一只大鸭子，大鸭子有多少只．
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<result>9</result>