Using the four numbers 0, 1, 2, and 3, one-digit numbers, two-digit numbers, three-digit numbers, and four-digit numbers can be used to form many natural numbers (in a number, each number is only used once), How many natural numbers are multiples of 3?
用0，1，2，3这四个数字，可以组成一位数，两位数，三位数，四位数，这样的很多自然数(在一个数里，每个数字只用1次)，其中是3的倍数的自然数共有多少个．
<gadget id="calculator">3 * 2 * 1</gadget>
<output>6</output>

<gadget id="calculator">3 * 6</gadget>
<output>18</output>

<gadget id="calculator">2 + 3 + 10 + 18</gadget>
<output>33</output>

<result>33</result>