There are a certain number of girls in a class, and they are divided into groups of 4 and 5, and there are no leftovers. How many girls are there at least in this class?
某班有女生若干人，分成4人一组，5人一组，都没有剩余，这个班女生至少有多少人？
<gadget id="calculator">4 * 5</gadget>
<output>20</output>

<result>20</result>