#!/usr/bin/perl

# http://perlmonks.org/?node_id=1211497

use strict;
use warnings;

sub up
  {
  my ($row, $col) = split /-/, $_[0];
  my ($startrow, $startcol) = split /-/, $_[-1];
  return $_[0] eq $_[-1] ? "@_[0..@_-2]\n" :
    ($row - $startrow > 0 && $col - $startcol > 0 &&
      up( ~-$row . '-' . ~-$col, @_ ) ) .
    ($row - $startrow > $col - $startcol &&
      up( ~-$row . '-' . $col, @_ ) );
  }

print up( '3-1', '1-0' ); # bottom, top