There are 20 yuan, buy mineral water, a bottle of water is 1 yuan, two empty bottles can be exchanged for a bottle of water. Excuse me, how many bottles of water do you drink at most?
有20元钱，买矿泉水，水一元一瓶，两个空瓶子可以换一瓶水．请问，最多喝几瓶水？
<gadget id="calculator">20 + 10 + 5 + 2 + 1 + 1</gadget>
<output>39</output>

<result>39</result>