The HSK curriculum has a total 112 idioms. With the exception of
讨价还价 and 名胜古迹 being in HSK 5, the rest 110
are all in HSK 6.
There are also 9 four-character phrases in the HSK that are obviously
not idioms: 公共汽车 电子邮件 高速公路 归根到底 二氧化碳 新陈代谢 烟花爆竹 迄今为止