There is a four-digit number, and the sum of it and its reverse four-digit number is 9999, for example, 7812+2187=9999, 3636+6363=9999, etc. How many such four-digit numbers are there?
有一个四位数，它与它的逆序四位数和为9999，例如7812+2187=9999，3636+6363=9999等，那么这样的四位数一共有多少个？
<gadget id="calculator">4 * 5 * 2 * 2</gadget>
<output>80</output>

<result>80</result>