Xiao Ming is going to use ribbons to surround a rectangle with a length of 5 meters and a width of 4 meters. How many meters of ribbons should he prepare at least?
小明准备用彩带围一个长5米，宽4米的长方形，他至少要准备多少米的彩带．
<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<result>18</result>