#include <bits/stdc++.h>
using namespace std;
using ll = long long;
template <class T> using vec = vector<T>;
template <class T> using vvec = vector<vec<T>>;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N;
    cin >> N;
    vec<ll> A(N),B(N);
    ll asum = 0,bsum = 0;
    for(auto& x:A){
        cin >> x;
        asum += x;
    }
    for(auto& x:B){
        cin >> x;
        bsum += x;
    }
    if(N==2){
        ll d0 = A[0]-B[0],d1 = A[1]-B[1];
        cout << ((d0+d1==0)? abs(d0):-1) << "\n";
        return 0;
    }
    if(asum<bsum){
        cout << -1 << "\n";
        return 0;
    }
    if((asum-bsum)%(N-2)!=0){
        cout << -1 << "\n";
        return 0;
    }
    ll ans = (asum-bsum)/(N-2);
    ll cnt = 0;
    for(int i=0;i<N;i++){
        ll d = B[i]-A[i];
        if((ans+d)%2){
            cout << -1 << "\n";
            return 0;
        }
        if(ans+d<0){
            cout << -1 << "\n";
            return 0;
        }
        cnt += (ans+d)/2;
    }
//    cerr << ans << " " << cnt << "\n";
    cout << (ans==cnt? ans:-1) << "\n";
}