一心 いっしん不乱 ふらん
isshin furan

Noun
na-Adjective

1. wholeheartedly; with heart and soul; intently; with undivided attention; with intense concentration; single-mindedly

Yojijukugo
自分 じぶん仕事 しごと一心 いっしん不乱 ふらん みなさい。
jibunno shigotoni isshin furanni uchikominasai.
Give yourself to your work with body and soul.