#include<bits/stdc++.h>

using namespace std;
using ll = long long;


int main()
{
    ll n;
    cin >> n;
    vector<ll> a(n), b(n);
    for(ll i = 0; i < n; i++)cin >> a[i];
    for(ll i = 0; i < n; i++)cin >> b[i];
    ll sum = 0, k = 0, use = 0;
    for(ll i = 0; i < n; i++) sum += (a[i] - b[i]);

    if(n == 2 && sum) {
        cout << -1 << endl;
        return 0;
    }else if(n == 2 && sum == 0) {
        cout << abs(a[0] - b[0]) << endl;
        return 0;
    }

    if(sum % (n - 2)) {
        cout << -1 << endl; return 0;
    }
    k = sum / (n - 2);
    for(ll i = 0; i < n; i++) {

        if((b[i] - a[i] + k) % 2 || (b[i] - a[i] + k) < 0) {
            cout << -1 << endl;
            return 0;
        }
        use += (b[i] - a[i] + k) / 2;
        
    }
    if(use != k) {
        cout << -1 << endl;
        return 0;
    }
    cout << k << endl;
}