Puzzle 222: Bite the Threes

This puzzle was introduced by Nikoli with a three-word japanese title.It is a region division puzzle similar to Shikaku.
Rules: Divide the grid into some regions,each region containing a given number that equals the size of the region. Every region whose size is a multiple of 3,should be rectangular,but with one of its corners cut off(L-shaped).All other regions should be strictly rectangular.