my %hash = ( 1=>2, 19=>20, 38=>50, 40=>10, 60=>3, 66=>80, 700=>1 );
my %sums = dosomemagic(\%hash);

print Dumper(\%sums);

#-----------------

sub dosomemagic
{
  my $hash=shift;
  my %return;

  my @keys=sort keys(%$hash);
  while(@keys>=4)
  {
    $return{$keys[0]}+=$hash{$keys[$_]} for(0..3);
    shift(@keys);
  }

  return %return;
}