#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

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

    int n;
    cin >> n;

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

    if (n == 2) {
        if (s == 0) {
            cout << abs(b[0] - a[0]) << endl;
        } else {
            cout << -1 << endl;
        }
        exit(0);
    }

    if (s % (n - 2) != 0 || s < 0) {
        cout << -1 << endl;
        exit(0);
    }

    ll r = s / (n - 2);

    for (int i = 0; i < n; i++) {
        ll t = r + b[i] - a[i];
        if (!(t >= 0 && t % 2 == 0)) r = -1;
    }

    cout << r << endl;

    //1回操作をする毎に全体の和はn-2だけ減る 可能であれば操作回数がわかる

    return 0;
}