A store stipulates that 3 empty Coke bottles can be exchanged for 1 bottle of soda without additional payment. Uncle Xiao Zhang bought 10 bottles of soda and didn’t spend any money. How many bottles of soda can he drink in total?
某商店规定，3个空可乐瓶可以换1瓶汽水，不用另付钱．小张叔叔买了10瓶汽水，不再花钱，他一共可以喝几瓶汽水？
<gadget id="calculator">10 + 3 + 1 + 1</gadget>
<output>15</output>

<result>15</result>