sub get_latest {
  my ($year, $mon, $day, $num) = @_;
  my @arr;
  
  if ($year && $mon && $day) {
    my $h = $d_dbd->{$year}->{$mon}->{$day};
    @arr = keys(%$h);
  }
  elsif ($year && $mon) {
    my $h = $d_dbd->{$year}->{$mon};
    FOO: for my $day (sort {$b <=> $a} (keys %$h)) {
      my $h = $d_dbd->{$year}->{$mon}->{$day};
      push(@arr, keys(%$h));
      last FOO if (scalar(@arr) > $num);
    }
  }
  elsif ($year) {
    my $h = $d_dbd->{$year};
    FOO: for my $mon (sort {$b <=> $a} (keys %$h)) {
      my $h = $d_dbd->{$year}->{$mon};
      for my $day (sort {$b <=> $a} (keys %$h)) {
        my $h = $d_dbd->{$year}->{$mon}->{$day};
        push(@arr, keys(%$h));
        last FOO if (scalar(@arr) > $num);
      }
    }
  }
  else {
    FOO: for my $year (sort {$b <=> $a} (keys %$d_dbd)) {
      my $h = $d_dbd->{$year};
      for my $mon (sort {$b <=> $a} (keys %$h)) {
        my $h = $d_dbd->{$year}->{$mon};
        for my $day (sort {$b <=> $a} (keys %$h)) {
          my $h = $d_dbd->{$year}->{$mon}->{$day};
          push(@arr, keys(%$h));
          last FOO if (scalar(@arr) > $num);
        }
      }
    }
  }

  return extract(\@arr, $num);
}