Choose three numbers from 0, 3, 4, 5 to form a three-digit number, how many such three-digit numbers are there?
在0、3、4、5中选三个数字组成三位数，这样的三位数有多少个．
<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<result>18</result>