sub get_date_by_week {
    my $week = shift || 1;
    my $year = shift || (localtime)[5];
    my $pattern = shift || '%d/%m';
    my $t = timegm(0, 0, 0, 1, 0, $year);
    my $w = (gmtime($t))[6];
    $w = ($w - 2) % 7 + 1;
    my $wc = $week * 7 - $w;
    return strftime($pattern, gmtime($t + $wc * 24 * 3600));
}