Uncle Zhang rides on the back of an ox to drive the ox across the river. There are four oxen A, B, C, and D in total. It takes 3 minutes for A ox to cross the river, 5 minutes for B ox to cross the river, 2 minutes for C ox to cross the river, and 2 minutes for D ox to cross the river. It takes 6 minutes to cross the river, and only 2 cows can be driven across the river at a time. How long will it take at least to drive all 4 cows to the other side of the river?
张大爷骑在牛背上赶牛过河，共有甲、乙、丙、丁四头牛，甲牛过河要3分钟，乙牛过河要5分钟，丙牛过河要2分钟，丁牛过河要6分钟，每次只能赶2头牛过河，要把这4头牛全部赶到河对岸去，最少要多少分钟．
<gadget id="calculator">3 + 2 + 6 + 3 + 3</gadget>
<output>17</output>

<result>17</result>