#!/usr/bin/perl

use strict;
use warnings;
use List::Util qw( min );

local $_ = <<END;
            1
           2 4
          6 4 9
         5 1 7 2
END
my @d = map [ split ], split /\n/;

my %cache;

print path(0, 0), "\n";

sub path
  {
  my ($r, $c) = @_;
  $cache{"@_"} //= $r < $#d
    ? $d[$r][$c] + min(path($r+1, $c), path($r+1, $c+1))
    : $d[$r][$c]
  }