#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(int)(n);i++)
using namespace std;
using ll = long long ;
using P = pair<int,int> ;
using pll = pair<long long,long long>;
constexpr int INF = 1e9;
constexpr long long LINF = 1e17;
constexpr int MOD = 1000000007;
constexpr double PI = 3.14159265358979323846;

int main(){
    ll n;
    cin >> n;
    vector<ll> a(n),b(n);
    rep(i,n) cin >> a[i];
    rep(i,n) cin >> b[i];
    ll suma = 0, sumb = 0;
    rep(i,n) suma += a[i];
    rep(i,n) sumb += b[i];

    if((suma-sumb)%(n-2)!=0||suma<sumb){
        cout << -1 << endl;
        return 0;
    }

    ll ans = (suma-sumb)/(n-2);

    ll sum = 0;
    bool ok = true;

    rep(i,n){
        if((b[i]-a[i]+ans)%2!=0||(b[i]-a[i]+ans)<0){
            ok = false;
            break;
        }
        else{
            sum += (b[i]-a[i]+ans)/2;
        }
    }

    if(ok&&sum==ans) cout << ans << endl;
    else cout << -1 << endl;

    return 0;
}