sub muri { print -1; exit; }

$n=<>;
@a=glob<>;
@b=glob<>;
for(0..$n-1){
	$s-=$b[$_]-=$a[$_];
}

$n==2 ? $s==0 : $s%($n-2)==0 or muri;

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

print "s=$s t=$t\n";
$s==$t or muri;
print $s;