How many non-repeating four-digit numbers can be formed using the four numbers 4, 7, 0, and 3?
用4、7、0、3这四个数，可以组成多少个不重复的四位数．
<gadget id="calculator">3 * 3 * 2 * 1</gadget>
<output>18</output>

<result>18</result>