The telephone number of a certain city is 75890001-75899999, how many telephones can be installed in this city at most.
某市的电话号码是75890001-75899999，这个城市最多可以安装多少部电话．
<gadget id="calculator">10 * 10 * 10 * 10</gadget>
<output>10_000</output>

<gadget id="calculator">10_000 - 1</gadget>
<output>9_999</output>

<result>9_999</result>