#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;
const long long INF = 1001001001;
const long long MOD = 1000000007;
const double EPS = 1e-10;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    ll n;
    cin>>n;
    ll a[n],b[n];
    for(int i=0;i<n;i++)cin>>a[i];
    for(int i=0;i<n;i++)cin>>b[i];
    ll diff=0;
    for(int i=0;i<n;i++)diff+=a[i]-b[i];
    if(n==2){
        if(a[0]-b[0]==b[1]-a[1])cout<<abs(a[0]-b[0])<<endl;
        else cout<<-1<<endl;
        return 0;
    }
    if(diff%(n-2)!=0){
        cout<<-1<<endl;
        return 0;
    }
    ll cnt=diff/(n-2);
    ll pls=0;
    for(int i=0;i<n;i++){
        ll d=a[i]-cnt;
        ll e=b[i]-d;
        if(e<0){
            cout<<-1<<endl;
            return 0;
        }
        pls+=e/2;
    }
    if(pls==cnt)cout<<cnt<<endl;
    else cout<<-1<<endl;
}