my @array=(1,2,3,4,-1,-2,-3,11,12,13);
my @sums=();
my $last=0;
map {
  push @sums, $last+$_ if $last>0 and $_>0;
  $last=$_;
} @array;
my $max=0;
map {$max=$_ if $_>$max } @sums;

print "Max sum: $max\n";