sub muri { print -1; exit; }

$n=<>;
@a=<>=~/\S+/g;
@b=<>=~/\S+/g;
for(0..$n-1){
	$s-=$b[$_]-=$a[$_];
}

if($n==2){
	$s==0 or muri;
	$t=abs$b[0];
}else{
	$s%($n-2)==0 or muri;
	$s/=$n-2;
	if($b[0]+$s&1){
		$d=$n-2;
	}
	for(0..$n-1){
		($b[$_]+=$d)+$s&1 and muri;
		$t+=$u=($b[$_]+$s)/2;
	}
	$s==$t or muri;
}

print $t;