#include <algorithm>
#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(x) (x).begin(), (x).end()
#define ll long long
#define ld long double
#define INF 1000000000000000000
typedef pair<ll, ll> pll;
typedef pair<int, int> pint;

int N;
bool isOK(ll key, vector<ll> A, vector<ll> B) {
    rep(i, N) { A[i] -= key; }

    ll cnt = 0;
    rep(i, N) {
        if (B[i] < A[i])
            return false;
        else
            cnt += (B[i] - A[i]);
    }

    if (cnt == 2 * key)
        return true;
    else
        return false;
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    cin >> N;
    vector<ll> A(N), B(N), P(N);
    ll suma = 0, sumb = 0;
    rep(i, N) {
        cin >> A[i];
        suma += A[i];
    }

    rep(i, N) {
        cin >> B[i];
        sumb += B[i];
    }

    if (N == 2) {
        if (A[0] - B[0] + A[1] - B[1] == 0)
            cout << abs(A[0] - B[0]) << endl;
        else
            cout << -1 << endl;
        return 0;
    }

    if ((suma < sumb) || ((suma - sumb) % (N - 2) != 0)) {
        cout << -1 << endl;
        return 0;
    }

    ll V = (suma - sumb) / (N - 2);
    ll cnt = 0;
    rep(i, N) { P[i] = B[i] - (A[i] - V); }

    rep(i, N) {
        if (P[i] % 2 == 1 || P[i] < 0) {
            cout << -1 << endl;
            return 0;
        };
        cnt += P[i];
    }

    if (cnt != 2 * V)
        cout << -1 << endl;
    else
        cout << V << endl;
    return 0;
}