sub smart {
    my $t=sum @_;
    if ($t%2) {
        my $i=($t-1)/2;
        ($i -= $_[$_])<0 and return $_ for 0..$#_;
    } else {
        my $i=$t/2-1;
        my ($found1, $found2);
        for (0..$#_) {
            ($found1=$_), last if ($i -= $_[$_])<0;
        }
        my $j=$t/2;
        for (0..$#_) {
            ($found2=$_), last if ($j -= $_[$_])<0;
        }
        return ($found1+$found2)/2;
    }
}