Transformation rule doesnt work

Hi,

I am trying to develop a transformation rule as folows:

IF( INPUT+0 ( 2 ) = 'XY', SYST-HOST, SYST-DATUM ) = doesnt work

IF( INPUT = 'XY', SYST-HOST, SYST-DATUM ) = works.

The first line is correct ABAP as far as I know, but doesnt work...Message "Invalid formula element: INPUT+0 "

What ist wrong, I even tried bracktes....?