<>;
push@{$_%2},$_ for glob<>;
@$_=sort{$a-$b}@$_ for 0,1;
<>=~/\d+ -?/;$z=$&+$';
if($z==0){
	exit!print 0
}
if(grep$_==$z,@0,@1){
	exit!print 1
}
for$m(0,1){
	$r=$z-$m&1;
	$i=$#r;
	for(@$m){
		$i--until!$i||$_+@$r[$i]<=3*$z;
		if($z<=$_+@$r[$i]&&$_+@$r[$i]<=3*$z){
			exit!print 2
		}
	}
}
print-1