The kindergarten bought a cart of watermelons. On the first day, divide the watermelon into 4 parts and eat 1 part; on the second day, divide the watermelon into 3 parts and eat 1 part; on the third day, divide the watermelon into 2 parts After eating one of them, he threw away 2 bad melons; on the fourth day, he ate the last 18. How many watermelons are there in this cart?
幼儿园买来一车西瓜．第一天把这车西瓜平均分成4份，吃了其中的1份；第二天把剩下的西瓜平均分成3份，吃了其中的l份；第三天把剩下的西瓜平均分成2份，吃了其中的1份后，还扔了2个坏瓜；第四天吃了最后18个．问这车西瓜一共有多少个？
<gadget id="calculator">18 + 2</gadget>
<output>20</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">20 / (3/4) / (2/3) / (1/2)</gadget>
<output>80</output>

<result>80</result>