There are a batch of books on the bookshelf. There are 81 known Chinese books and math books, 83 math books and foreign language books, 86 foreign language books and extracurricular books, and there are 2 more Chinese books than extracurricular books. So how many foreign language books are there?
书架上有一批书，已知语文书和数学书共有81本，数学书和外语书共有83本，外语书和课外书共有86书，语文书比课外书多2本．那么外语书有多少本？
<gadget id="calculator">126 - 81</gadget>
<output>45</output>

<result>45</result>