crystal report function

CREATE FUNCTION [dbo].[GLAS_AGING]
( @tnum int,
@flag VARCHAR(1))
RETURNs int as
BEGIN
declare @result int
begin
IF @flag = 'Y' AND @tnum > 999
set @result= 8

IF @tnum<=30
set @result= 0

IF @tnum <= 90
set @result=1

IF @tnum > 90 AND @tnum <= 180
set @result=2

IF @tnum > 180 AND @tnum <= 365
set @result= 3

IF @tnum > 365 AND @tnum <= 545
set @result= 4

IF @tnum > 545
set @result= 5
end
return @result

END
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this is function how to invoke this function to crystal report in asp.net.....
how to create in crystal report formula editor?