I think you might mean one of the following:
The floor function: \(\lfloor 2x/3 \rfloor + 3\)
or the ceiling function: \(\lceil 2x/3 \rceil + 3\)
where the floor function is the nearest integer below the value of the argument and the ceil function is the nearest integer above the value of the argument. Notice that the lines are not [ or ]; i.e. they are not the same as standard square brackets.
In the graph below f(x) is the floor function and g(x) is the ceiling function:
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