not buy and...
その本は買わなくてもよかったのに。
You didn't have to buy that book.
水をマレーシアから買わなくてはならないのです。
We have to buy water from Malaysia.
新しいスキーを一組買わなくてはなりません。
I have to buy a new pair of skis.
外国から買わなくてはなりません。
We have to buy it from abroad.
こんなものを買わなくてよかった。
I'm glad I didn't buy something like this.
そんな高い本買わなくてもよかったのに。
You didn't have to buy such an expensive book.