A cow-herding boy wants to drive 4 cows across a river, and only 2 cows can be driven at a time. It takes 1 minute for cow A to cross the river, 2 minutes for cow B to cross the river, 4 minutes for cow C to cross the river, and 4 minutes for cow D to cross the river. It takes 5 minutes, how many minutes does it take at least for the cowherd boy to drive 4 cows across the river?
一个放牛娃要将4头牛赶过一条河，每次只能赶2头，甲牛过河需1分钟，乙牛过河需2分钟，丙牛过河需4分钟，丁牛过河需5分钟，放牛娃将4头牛赶过河最少需几分钟？
<gadget id="calculator">1 + 2 + 2 + 5 + 2</gadget>
<output>12</output>

<result>12</result>