Then take an empty bus and walk 5+ 18=23 people.

Only 1 23 can be divided by 23.

The remaining cars are either 1 or 23.

1+ 1=2 cars

1+23= 14 cars

2× 18+5=4 1 person

Or 24× 18+5=437 people.

"All teachers and students in a middle school" I think the latter is desirable:

There used to be 24 buses and 437 teachers and students in the school.