There are several footballs laid out in a row, the distance between two adjacent footballs is 5m, and the distance between the two most edge footballs is 50m. How many footballs are there between them?
有若干个足球一字摆开，相邻的两个足球间都相距5m，最边缘的两个足球相距50m，问它们之间还有多少个足球？
<gadget id="calculator">50 / 5</gadget>
<output>10</output>

<gadget id="calculator">1 - 2</gadget>
<output>-1</output>

<gadget id="calculator">10 + (-1)</gadget>
<output>9</output>

<result>9</result>