There's a problem with your 2nd formula. If Number = -3892.1, it gives -3894. If Number = 0, the
result is -1.
To round a positive number down and a negative number up, you can use FIX, i.e.
=FIX(Number)
You can also use the worksheet functions ROUNDUP and ROUNDDOWN, as well as ROUND.
With Number = -3892.1, Fix, Round, and RoundDown all give -3892. RoundUp gives -3893.