The page numbers of a book are 1, 2, 3..., and the middle page is torn off, and the sum of the remaining page numbers is exactly 2007, so what is the number of the torn-off page?
一本书的页码为1，2，3…，她的中间一页被撕掉了，余下的各页码之和正好是2007，则被撕掉的页是第多少页．
<gadget id="calculator">4 - 5</gadget>
<output>-1</output>

<result>-1</result>