45 students go to the garden and want to buy mineral water, and buy 4 bottles and get 1 free in the store, so how many bottles do they only need to pay for?
45名学生去游园，要买矿泉水，商店买4瓶送1瓶，那么他们只需要付钱的有多少瓶？
<gadget id="calculator">9 * 4</gadget>
<output>36</output>

<result>36</result>