遺憾 いかん千万 せんばん
ikansen ban

na-Adjective

1. highly regrettable; utterly deplorable

Yojijukugo
きみがそれを らないのは遺憾 いかん せん まんだ。
kimiga soreo shiranai nowa ikan semmanda.
It is a great pity that you don't know it.