my @kw = sort qw( ze ez zl lz ze );
my @dw = sort qw( ze ez ze ez zd );

my $c = 0;
my $kw_i = 0;
my $dw_i = 0;
while ($kw_i < @kw && $dw_i < @dw) {
   if ($kw[$kw_i] lt $dw[$dw_i]) { ++$kw_i; next; }
   if ($dw[$dw_i] lt $kw[$kw_i]) { ++$dw_i; next; }
   ++$c;
   ++$kw_i;
   ++$dw_i;
}