The school library bought more than 1,800 volumes of three kinds of books. Among them, there are 250 science and technology books, 320 more story books than science and technology books, and the rest of the teaching reference books. How many volumes of teaching reference books should I buy?
学校图书馆买来三种图书共计1800余册．其中科技书250册，故事书比科技书多320册，其余的教学参考书．买教学参考书多少册？
<gadget id="calculator">250 + 320</gadget>
<output>570</output>

<gadget id="calculator">1_800 - 250 - 570</gadget>
<output>980</output>

<result>980</result>