The natural numbers 12321, 90009, 41014... have a common feature: they are written upside down and are the original numbers, so how many five-digit even numbers with this "characteristic" are there?
自然数12321，90009，41014…有一个共同特征：它们倒过来写还是原来的数，那么具有这种"特征"的五位偶数有多少个．
<gadget id="calculator">4 * 10 * 10</gadget>
<output>400</output>

<result>400</result>