def elapsed_time_format(seconds):
    """Returns human readable string for elapsed time"""
    negative = seconds < 0
    seconds = abs(int(seconds))
    periods = [
        ('year', 60 * 60 * 24 * 365),
        ('month', 60 * 60 * 24 * 30),
        ('day', 60 * 60 * 24),
        ('hour', 60 * 60),
        ('minute', 60),
        ('second', 1)
    ]

    strings = []
    for period_name, period_seconds in periods:
        if seconds >= period_seconds:
            period_value, seconds = divmod(seconds, period_seconds)
            if period_value == 1:
                strings.append('{} {}'.format(period_value, period_name))
            else:
                strings.append('{} {}s'.format(period_value, period_name))

    message = ', '.join(strings)
    if not message:
        message = "0 seconds"

    if negative:
        return 'Negative ' + message
    return message