Xiao Ming rides on the back of an ox to drive four buffaloes across the river. It takes 2 minutes, 3 minutes, 6 minutes, and 8 minutes for the four oxen to cross the river respectively, and he can only drive two oxen across the river at a time. So how many minutes does Xiao Ming need at least to drive all the cattle across the river?
小明骑在牛背上要赶着四头水牛过河，这四头牛过河分别需要2分、3分、6分、8分钟，并且每次只能赶着两头牛过河．那么小明至少需要多少分钟才能把牛全部赶过河去．
<gadget id="calculator">3 + 2 + 8 + 3 + 3</gadget>
<output>19</output>

<result>19</result>