死刑囚、魔法学校にて教鞭を振るう = Convict on death row,teaching at a magic school
しけいしゅう まほう がっこう にて きょうべん お ふるう
est. Rough estimate based on volume count, reprints and magazine — not an official figure
How to compare editions, collected volumes and ISBNs / Sources, updates and corrections