~なければなりません (polite must)

We have to find the money somehow, Mr. Chairman. It's for the children.

Under this system, students must take turns teaching each other and helping one another.

You have to be ready for the unexpected.

You should avoid visiting others without an appointment.

I have to sleep.

And then you have to pass through inspection by an immigration officer and receive permission to land.

You have to close the gate at night.