#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<long long> vl;
#define INF __INT32_MAX__
#define LINF __LONG_LONG_MAX__

int main() {
    int N;
    cin >> N;
    vl A(N), B(N);
    rep(i, N) { cin >> A[i]; } 
    rep(i, N) { cin >> B[i]; } 
    ll suma = 0, sumb = 0;
    rep(i, N) { suma += A[i]; sumb += B[i]; }

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

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

    rep(i, N) {
        A[i] -= cnt;
    }

    bool ok = true;
    ll sum = 0;
    rep(i, N) {
        if (A[i] > B[i]) {
            ok = false;
            break;
        }
        sum += (B[i] - A[i]);
    }
    if (sum != 2 * cnt) ok = false;

    if (ok) {
        cout << cnt << endl;
    } else {
        cout << -1 << endl;
    }
}