#include <bits/stdc++.h>
using namespace std;
#define int long long
typedef pair<int,int> P;
int INF = 1e9+7;
int mod = 1e9+7;
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
signed main() {
    int N;
    cin >> N;
    vector<int>A(N);
    vector<int>B(N);
    int sumA = 0;
    for(int i = 0; i < N; i++) {
        cin >> A[i];
        sumA+=A[i];
    }
    int sumB = 0;
    for(int i = 0; i < N; i++) {
        cin >> B[i];
        sumB+=B[i];
    }
    if(sumA < sumB) {
        cout << -1 << endl;
        return 0;
    }
    if(N == 2) {//%0はできないため
        if(sumA != sumB) cout << -1 << endl;
        else cout << abs(A[0]-B[0]) << endl;
        return 0;
    }
    if((sumA-sumB)%(N-2) != 0) {
        cout << -1 << endl;
        return 0;
    }
    int K = (sumA-sumB)/(N-2);
    int cnt = K;//後何回操作できるか
    for(int i = 0; i < N; i++) {
        if(A[i]-K <= B[i]) {
            if((B[i]-(A[i]-K))/2 > cnt) {
                cout << -1 << endl;
                return 0;
            }
            cnt-=(B[i]-(A[i]-K))/2;
        }
        else {
            cout << -1 << endl;
            return 0;
        }
    }
    if(cnt != 0) {
        cout << -1 << endl;
    }
    else {
        cout << K << endl;
    }
}