This is a floor function graph

For any x, floor (x) is defined as the greatest integer less than or equal to x

For example, let x = 3 ....so....

floor (3) = 3

So

floor(3) - 3 = 0

And let x = 2.5 .....so....

floor (2.5) = 2

So

floor (2.5) - 3 = 2 - 3 = -1

The last graph is correct