After adding zeros at the end of a four-digit number, subtract the original four-digit number from the resulting number. The difference is 621819. Find the original four-digit number.
在一个四位数的末尾添零后，把所得的数减去原有的四位数，差是621819，求原来的四位数．
<gadget id="calculator">100 - 1</gadget>
<output>99</output>

<gadget id="calculator">621_819 / 99</gadget>
<output>6_281</output>

<result>6_281</result>