In order to recycle wine bottles, the brewery stipulates that every 3 wine bottles can be exchanged for 1 bottle of beer. Uncle Xiao Ding bought 20 bottles of beer, and after drinking them, he exchanged the empty bottles for wine. How many bottles of beer can he drink in total?
啤酒厂为了回收酒瓶，规定每3个酒瓶可以换1瓶啤酒．小丁叔叔买了20瓶啤酒，喝完之后，又拿空瓶换酒喝，他一共可以喝到多少瓶啤酒．
<gadget id="calculator">20 + 7 + 2 + 1</gadget>
<output>30</output>

<result>30</result>