def lfnGroup(job):
    """
    _lfnGroup_

    Determine the lfnGroup from the job counter and the agent number
    provided in the job baggage, the job counter and agent number
    default both to 0. The result will be a 5-digit string.
    """
    modifier = str(job.get("agentNumber", 0))
    jobLfnGroup = modifier + str(job.get("counter", 0) // 1000).zfill(4)
    return jobLfnGroup