#include <bits/stdc++.h>
#define rep(a,n) for (ll a = 0; a < (n); ++a)
using namespace std;
typedef long long ll;
typedef pair<ll,ll> P;
typedef pair<P,P> PP;
typedef vector<vector<ll> > Graph;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
const ll INF = 1e18;

int main(){
    int n;
    cin >> n;
    vector<ll>a(n),b(n);
    ll sa=0,sb=0;
    rep(i,n){
        cin>>a[i];
        sa+=a[i];
    }
    rep(i,n){
        cin>>b[i];
        sb+=b[i];
    }
    if(sa<sb){
        cout << -1 << endl;
        return 0;
    }
    if(n==2){
        if((sa+sb)%2==0){
            cout << abs(a[0]-b[0]) << endl;
            return 0;
        }
        else{
            cout << -1 << endl;
            return 0;
        }
    }
    if((sa-sb)%(n-2)!=0){
        cout << -1 << endl;
        return 0;
    }
    ll c = (sa-sb)/(n-2);
    rep(i,n){
        ll ci = a[i]-b[i]+c;
        if(ci<0||ci%2==1){
            cout << -1 << endl;
            return 0;
        }
    }
    cout << c << endl;
    return 0;
}