sub intersect { 
	my ($a,$b,$c,$d) = @_; 
	my ($n1,$n2) = ([$a,$b],[$c,$d]); 
	if($a > $c){ 
		my $t = $n1; 
		$n1 = $n2; 
		$n2 = $t; 
		}
	($a,$b,$c,$d) = (@n1,@n2); 
	return ($b-$c)*($b>$c)-($b-$d)*($b>$d); 
	}