#!/usr/bin/perl

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

use strict;
use warnings;

sub up
  {
  my ($x, $y) = split /-/, $_[0];
  $x && $y and up( $x - 1 . '-' . ($y - 1), @_ );
  $x and up( $x - 1 . "-$y", @_ );
  $x || $y or print "@_\n";
  }

up( '3-1' );