How to return string value from the stored procedure

Alter procedure S_Comp(@str1 varchar(20),@r varchar(100) out)
as
declare  @str2 varchar(100)
set @str2  ='welcome to sql server. Sql server is a product of Microsoft'
if(PATINDEX('%'+@str1 +'%',@str2)>0)
    return @str1+'present in the string'
else 
    return @str1+'not present'

I am executing the above stored procedure. I am getting the following error :

Msg 245, Level 16, State 1, Procedure S_Comp, Line 8 Conversion failed when converting the varchar value 'Amruthanot present' to data type int.

Please do help me resolving this