#include<bits/stdc++.h>
using namespace std;
using ll = long long;

int main() {
	ll n;
	cin >> n;
	vector<ll> a(n);
	for (ll i = 0; i < n; ++i)cin >> a[i];
	for (ll i = 0; i < n; ++i) {
		ll b;
		cin >> b;
		a[i] -= b;
	}
	if (n == 2) {
		if (a[0] + a[1] == 0)cout << abs(a[0]) << endl;
		else cout << -1 << endl;
		return 0;
	}
	ll sum = accumulate(a.begin(), a.end(), 0ll);
	if (sum % (n - 2) != 0 || sum < 0) {
		cout << -1 << endl;
		return 0;
	}
	sum /= n - 2;
	for (ll i = 0; i < n; ++i) {
		if ((sum + a[i]) % 2 != 0) {
			cout << -1 << endl;
			return 0;
		}
		if (a[i] - sum > 0 || a[i] + sum < 0) {
			cout << -1 << endl;
			return 0;
		}
	}
	cout << sum << endl;
}