Students go rowing, if there are 4 people in a boat, there will be 1 more person, and every 5 people in a boat will also have 1 more person, ask at least how many classmates went?
同学们去划船，如果每4人一条船则多1人，每5人一条船也多1人，问至少去了多少个同学？
<gadget id="calculator">4 * 5</gadget>
<output>20</output>

<gadget id="calculator">20 + 1</gadget>
<output>21</output>

<result>21</result>