The 12 washed towels are clamped on the lead wire with clips. Both sides of each towel must be clamped, and the same clamp can clamp both sides of two towels. Now, what is the minimum number of clips needed to divide these towels into four layers.
洗好的12块毛巾用夹子夹在铅丝上．每一块毛巾的两边必须用夹子夹住，同一个夹子可以夹住两块毛巾的两边．现在，把这些毛巾分成四层至少需要多少个夹子．
<gadget id="calculator">1 + 2 + 1</gadget>
<output>4</output>

<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<result>16</result>