Xiao Ming's father dug a rectangular vegetable field by the river, 12 meters long and 6 meters wide. He used fences to enclose the three sides that are not near the river. How many meters of fences should be used at least?
小明的爸爸在河边挖了一块长方形菜地，长12米，宽6米．他用篱笆把不靠河边的三面围了起来，至少得用多少米篱笆？
<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<gadget id="calculator">12 + 12</gadget>
<output>24</output>

<result>24</result>