$hh{2}{6}{4} = -1;
$hh{3}{5}    = -1;
$hh{99}      = -1;
use Data::Dumper;
print Dumper( \%hh);
__END__
$VAR1 = {
          '99' => -1,
          '3' => {
                   '5' => -1
                 },
          '2' => {
                   '6' => {
                            '4' => -1
                          }
                 }
        };