Agent Job Failed

[[GM]Xia]

declare @extraName varchar(5) = ' '
declare @date1 datetime='15/06/2015 17:43'
DECLARE @disk_shard varchar(max)
set @disk_shard =('C:\Backups\SHARD\'+@extraName+'-Shard_DB_'+@date1+'.bak')


BACKUP DATABASE SRO_VT_SHARD
TO DISK = @disk_shard
WITH FORMAT,
MEDIANAME = 'SRO_VT_SHARD',
NAME = 'SRO_VT_SHARD'

what i try to do is each backup the Sql agent will make will create separate bak with date and time

we speak here on Microsoft Sql Server 2012 enterprise​