sub calc{
 my ($part) = @_;
 while($part =~ s!(\d+)\s*([\*\/])\s*(\d+)!subcalc($1,$2,$3)!eg){};
 while($part =~ s!(\d+)\s*([\+\-])\s*(\d+)!subcalc($1,$2,$3)!eg){};
 return $part;
}