Xiao Ming added the page numbers of a book page by page starting from 1, and added them to the end, and the number he got was 4979. Later, he found that there was a missing page in the book (two consecutive page numbers). So, how many pages are there in this book?
小明把一本书的页码从1开始逐页相加，加到最后，得到的数是4979，后来他发现这本书中缺了一张(连续两个页码)．那么，这本书原来有多少页．
<result>100</result>