Uncle Zhang packed the harvested ginger in the same big bag, a total of 40 bags. He weighed 4 of them, and the results were 18 kg, 21 kg, 19 kg, and 23 kg. How many kilograms of ginger did he harvest in total?
张大叔把收获的生姜装在同样大的袋子里，一共装了40袋．他称了其中的4袋，结果分别是18千克、21千克、19千克、23千克．他大约一共收获生姜多少千克？
<gadget id="calculator">20 * 40</gadget>
<output>800</output>

<result>800</result>