SQL Server Function for GetLastDayOfMonth

CREATE FUNCTION [dbo].[fn_GetLastDayOfMonth]     
(    
@InputDate datetime    
)    
RETURNS datetime    
BEGIN    
    RETURN DATEADD(day, -1, DATEADD(month, 1, CAST(CAST(YEAR(@InputDate) AS char(4)) + '/' + CAST(MONTH(@InputDate) AS char(2)) + '/01' AS datetime)))    
END