There are 5.22 million story books in the library, 5.2 million more than literature and art books. The number of science and technology books for children is exactly twice that of literature and art books. How many thousands of science and technology books are there in the school library?
图书室有故事书522万本，比文艺书多520万本，少儿科技书的本数正好是文艺书的2倍，学校图书室共有科技书多少万本？
<gadget id="calculator">522 - 520</gadget>
<output>2</output>

<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<result>4</result>