Avoiding uage of prefix sp_ improves the performance
When a stored procedure is executed using "sp_", SQL Server checks in the master first, as "sp_" is assumed to be reserved for a system stored procedure. Thus, the performance improvemnet would be caused by not having to go to the system to look first for the procedure.
In this case, executing the procedure as written causes the process to be executed from the master (system) where the code is
SELECT @Input + 2 AS Result
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