A six-digit number is composed of 1, 2, 3, 4, 5, and the difference between any two adjacent digits is 1. How many such six-digit numbers are there?
一个六位数由1、2、3、4、5组成，而且任意相邻两个数位的数字之差都是l，这样的六位数有多少个？
<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<gadget id="calculator">18 * 2</gadget>
<output>36</output>

<gadget id="calculator">18 + 36 + 18</gadget>
<output>72</output>

<result>72</result>