def chart_title(statistic, chat, start_date, end_date):
    """Return title for chart displaying statistic (given as string)."""
    return '{statistic} in "{subject}" ({start_date} - {end_date})'.format(
        statistic=statistic,
        subject=chat.subject,
        start_date=start_date.Format('%d/%m/%Y'),
        end_date=end_date.Format('%d/%m/%Y'))