#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (int)(n); i ++)
#define irep(i,n) for (int i = (int)n - 1;i >= 0;--i)
using namespace std;
using ll = long long;
using PL = pair<ll,ll>;
using P = pair<int,int>;
constexpr int INF = 1000000000;
constexpr long long HINF = 1000000000000000;
constexpr long long MOD = 1000000007;// = 998244353;
constexpr double EPS = 1e-4;
constexpr double PI = 3.14159265358979;

int main() {
    int N; cin >> N;
    vector<ll> A(N),B(N);
    rep(i,N) cin >> A[i];
    rep(i,N) cin >> B[i];
    ll tota = 0,totb = 0;
    rep(i,N) tota += A[i];
    rep(i,N) totb += B[i];
    if (N == 2) {
        if (tota == totb) {
            cout << abs(A[0] - B[0]) << '\n';
        }
        else {
            cout << -1 << '\n';
        }
        return 0;
    }


    if ((tota - totb)%(N - 2) != 0) {
        cout << -1 << '\n';
        return 0;
    }
    ll cnt = (tota - totb)/(N - 2);
    rep(i,N) {
        A[i] -= cnt;
    }
    ll time = 0;
    rep(i,N) {
        if (B[i] - A[i] < 0) {
            time = -1;
            break;
        }
        time += (B[i] - A[i])/2;
    }
    if (time == cnt) {
        cout << cnt << '\n';
    }
    else {
        cout << -1 << '\n';
    }
    return 0;
}