How many natural numbers are there greater than 500,000 and less than 510,000?
大于50万，小于51万的自然数有多少个．
<gadget id="calculator">509_999 - 500_001</gadget>
<output>9_998</output>

<gadget id="calculator">9_998 + 1</gadget>
<output>9_999</output>

<result>9_999</result>