Xiao Ming's father dug a rectangular vegetable field by the river, 8 meters long and 5 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8米，宽5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">5 * 2</gadget>
<output>10</output>

<gadget id="calculator">8 + 10</gadget>
<output>18</output>

<result>18</result>