# Pass list of filenames as arguments
 sub listnumbers {
  my %files;
  foreach (@_) {
   next unless (/^elmo(\d+)\.txt$/);
   my $n = int($1); # Force string to integer
   $files{$n} = $_;
  }
  # Did we wrap-around? This happens iff we have a 0 and a
  # 9999
  if (exists($files{0}) && exists($files{9999})) {
   # OK, so this is the tricky case
   # Count down from 9999 to find the first file
   my $lwm = 9999;
   while (exists($files{$lwm})) {
     --$lwm;
     die "I think something broke" if ($lwm < 5000);
   }
   # And count up from 0 to get the last file
   my $hwm = 0;
   while (exists($files{$hwm})) {
    ++$hwm;
    die "I think something broke" if ($hwm > 5000);
   }
   # And return the intervals
   ($lwm+1..9999, 0..$hwm-1);
  }
  else {
   # Easy case
   sort keys %files;
  }
 }
 # Main code
 my @numbers = listnumbers(<>);
 my $lastkey = read_lastkey();
 my $foundlast = 0;
 foreach (@numbers) {
  if ($_ == $lastkey) {
   $foundlast = 1;
   next;
  }
  if ((($_ + 1) % 10000) == $lastkey) {
   $foundlast = 1;
  }
  if ($foundlast) {
    process_file(sprintf("elmo%04d.txt", $_));
    $lastkey = $_;
  }
 }
 if ($foundlast) {
  write_lastkey($lastkey);
 }
 else {
  die "Didn't find a plausible sequel to $lastkey in [@numbers]";
 }