Some numbers such as 22, 131, 484, 3663, 7997...Reading from left to right is the same as reading from right to left. We call these numbers symmetrical numbers. How many symmetrical numbers are there in the four-digit number?
有些数如22、131、484、3663、7997…从左往右读与从右往左读是一样的，我们把这些数叫做对称数，在四位数中共有多少个对称数．
<gadget id="calculator">9 * 10</gadget>
<output>90</output>

<result>90</result>