my %next;
@next{0..9,'a'..'y','A'..'Y'} = (1..9,'a'..'z','B'..'Z');

sub inc36 {
  my ($l, $i, $r) = shift=~/^(.*?)([^zZ]?)([zZ]*)$/;

  $l . $next{ $i||0 } . (0 x length $r)
}