Page not found (404)

Request Method: GET
Request URL: http://mongolbooks.com/%D0%BD%D0%BE%D0%BC%D1%83%D1%83%D0%B4/%D1%81%D0%BE%D1%91%D0%BB-%D1%81%D1%83%D0%B4%D0%BB%D0%B0%D0%BB/

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.