#include <algorithm>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
using namespace std;
#define rep(i, n) for(int(i) = 0; (i) < (n); (i)++)
#define FOR(i, m, n) for(int(i) = (m); (i) < (n); (i)++)
#define All(v) (v).begin(), (v).end()
#define pb push_back
#define MP(a, b) make_pair((a), (b))
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
const int INF = 1 << 30;
const ll LINF = 1LL << 60;
const int MOD = 1e9 + 7;

int main() {
    int N;
    cin >> N;
    vector<ll> A(N), B(N);
    ll Asum = 0, Bsum = 0;
    rep(i, N) {
        cin >> A[i];
        Asum += A[i];
    }
    rep(i, N) {
        cin >> B[i];
        Bsum += B[i];
    }
    if(N == 2) {
        if(Asum == Bsum) {
            cout << abs(A[0] - B[0]) << endl;
        } else {
            cout << -1 << endl;
        }
        return 0;
    }
    if(Asum - Bsum < 0 || (Asum - Bsum) % (N - 2) != 0) {
        cout << -1 << endl;
        return 0;
    } else {
        int count = (Asum - Bsum) / (N - 2);
        rep(i, N) { A[i] -= count; }
        bool ok = 1;
        int cnt = 0;
        rep(i, N) {
            ll d = B[i] - A[i];
            if(d < 0 || d % 2 != 0)
                ok = 0;
            cnt += d / 2;
        }
        if(ok && cnt == count) {
            cout << count << endl;
        } else {
            cout << -1 << endl;
        }
    }
    return 0;
}