Obanma, Koizumi, Xiaomei, and O'Ou each took a bucket to collect water from a faucet at the same time, and they could only collect water one by one. To fill a bucket of water, it takes 7 minutes for Ao Zema, 5 minutes for Koizumi, 3 minutes for Xiaomei, and 2 minutes for Ouou. What is the minimum sum of the time it takes them to finish fetching water?
奥班马、小泉、小美、欧欧各拿一只水桶同时到一个水龙头前接水，他们只能一个一个地接水．打满一桶水，奥斑马要7分钟，小泉要5分钟，小美要3分钟，欧欧要2分钟．他们打完水的时间总和最少是多少分钟．
<gadget id="calculator">2 * 4</gadget>
<output>8</output>

<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<gadget id="calculator">8 + 9 + 10 + 7</gadget>
<output>34</output>

<result>34</result>