Among the four-digit number, how many numbers are equal to the original number and the reversed number (for example: the reversed number of 1543 is 3451).
四位数中，原数与反序数(例如：1543的反序数是3451)相等的共有多少．
<gadget id="calculator">9 * 10</gadget>
<output>90</output>

<result>90</result>