@c = sort { $b <=> $a } @c;

my $lr_len = 0;
my $lr_idx;

my $s = 0;
while ($s <= 4) {
   my $e = $s+1;
   ++$e while $e <= 4 && $c[$e] == $c[$e-1] - 1;
   if ($e-$s > $lr_len) {
      $lr_len = $e-$s;
      $lr_idx = $s;
   }
   $s = $e;
}