少なくとも

The adverb 少なくとも can be used with nouns or numbers to express "at (the) least" or "to say the least." The particle は can follow the noun or number/counter to further emphasize that word.

どんなに忙しくても、少なくとも6時間は寝た方がいいですよ。
No matter how busy you are, you should get at least 6 hours of sleep.

来年は、少なくとも3つは授業を取らなければいけない。
Next year, I have to take at least three classes.

人に何かしてもらったら、少なくともお礼は言った方がいい。
If someone gives you something, you should at least tell them thank you.

このことについては、少なくとも先生には話をしておいた方がいいと思う。
As for that matter, I think you should at least have a talk with sensei about it.