#include <bits/stdc++.h>
using namespace std;

void fail(){
    cout << -1 << endl;
    exit(0);
}

int main(){
    int N;
    cin >> N;
    vector<int64_t> A(N);
    for(int i=0; i<N; i++) cin >> A[i];
    for(int i=0; i<N; i++){
        int a;
        cin >> a;
        A[i] = a-A[i];
    }
    auto S = accumulate(A.begin(), A.end(), 0LL);
    if(S > 0) fail();
    if(N == 2){
        if(S) fail();
        cout << abs(A[0]) << endl;
        return 0;
    }
    if(S%(N-2)) fail();
    int64_t T = -S/(N-2);
    int64_t t = 0;
    for(int64_t a : A){
        a -= T;
        if(a > 0 || a%2) fail();
        t += -a/2;
    }
    if(t == T) fail();
    cout << T << endl;
    return 0;
}