Xiao Ming added up the page numbers of his book, from 1 to the last page, the total is 1050, but he found that he added one page repeatedly, how many pages are there.
小明把自己的书页码相加，从1开始加到最后一页，总共为1050，不过他发现他重复加了一页，请问是多少页．
<result>15</result>