If 4 empty mineral water bottles can be exchanged for one bottle of mineral water, there are currently 15 empty mineral water bottles, and the maximum amount of mineral water you can drink without paying.
如果4个矿泉水空瓶可以换一瓶矿泉水，现有15个矿泉水空瓶，不交钱最多可以喝矿泉水多少．
<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<result>5</result>