my %hash = (1=>2, 19=>20, 38=>50, 40=>10, 60=>3, 66=>80, 700=>1);
my @keylist = sort { $a <=> $b } keys %hash;
for (my $x=0; $x<=$#keylist-3; $x++){
        $hash{$keylist[$x]} += $hash{$keylist[$x+$_]} for (1..3);
}