#include <bits/stdc++.h>

using namespace std;

using ll = long long;

constexpr char newl = '\n';

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

    int n;
    cin >> n;

    vector<ll> a(n);
    ll suma = 0;
    for (int i = 0; i < n; i++) {
        cin >> a[i];
        suma += a[i];
    }

    vector<ll> b(n);
    ll sumb = 0;
    for (int i = 0; i < n; i++) {
        cin >> b[i];
        sumb += b[i];
    }

    ll diff = suma - sumb;
    if (n == 2) {
        cout << (diff == 0 ? abs(a[0] - b[0]) : -1) << newl;
        return 0;
    }
    
    if (diff < 0 || diff % (n - 2) != 0) {
        cout << -1 << newl;
        return 0;
    }

    ll cnt = diff / (n - 2);
    for (int i = 0; i < n; i++) {
        a[i] -= cnt;
    }

    for (int i = 0; i < n; i++) {
        ll tmp = b[i] - a[i];
        if (tmp < 0 || tmp % 2 != 0) {
            cout << -1 << newl;
            return 0;
        }
    }
    cout << cnt << newl;

    return 0;
}