There are some four-digit numbers such as: 1234, 1004, 8994, 9939, etc., and the sum of their digits is a multiple of 5. How many such four-digit numbers are there?
有一些四位数如：1234、1004、8994、9939等，它们的各位数字之和是5的倍数，这样的四位数一共有多少．
<gadget id="calculator">9_000 / 5</gadget>
<output>1_800</output>

<result>1_800</result>