#! perl -slw
use strict;
use threads;

my @words = do{ local( @ARGV, $/ ) = 'your.dictionary'; <> };
chomp @words;
my %dict;
undef @dict{ @words };

my $errors = 0;
my $savedfh;
my @files = glob "*";

open $savedfh, '<', shift( @files ) or die $!;
for my $file ( @files ) {
    my $fh = $savedfh;
    my $thread = async{ open my $fh, '<', $file or die $!; $fh };

    map +( exists $dict{$_} || ++$errors ), split while <$fh>;

    $savedfh = $thread->join;
}
print $errors;