Page not found (404)

Request Method: GET
Request URL: http://mongolbooks.com/%D1%85%D0%BE%D0%B2%D0%BE%D1%80-%D0%BD%D0%BE%D0%BC/

Шүүлтүүрт таарах slug олдсонгүй

You're seeing this error because you have DEBUG = True in your Django settings file. Change that to False, and Django will display a standard 404 page.