8 kyu?
the task is not too hard.
even iam a newbie can do this.

the problem was only in math.ceil cause i know only round and floor, and in zero input
formula isnt hard, people(not programmers of mathematics) do this everyday when choose wallpapers

to those who writes about ceiling and floor
Omg! its a wallpaper! not floorpaper or ceilingpaper! wtf!