WordPress adds -2 to the Page name

Ok so this is really weird, I want to call my page a number so it will be like this http://www.mysite.com/100 . this thing is, everytime I type a number as the page’s name, WordPress a “-2” to its end (so it will be mysite.com/100-2). It’s only happen when calling the page a number. and yeah it happens even if I choose totally random number like 921391293, so its not becuse that number already exsit. (there are only 5 pages in my site anyway). any ideas what I can do?