#pragma GCC optimize("O3")
#include <bits/stdc++.h>
#define ll long long
#define rep(i,n) for(ll i=0;i<(n);i++)
#define pll pair<ll,ll>
#define pq priority_queue
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define ios ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);
#define lb(c,x) distance(c.begin(),lower_bound(all(c),x))
#define ub(c,x) distance(c.begin(),upper_bound(all(c),x))

using namespace std;

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=1e9+7;

int main(){
    ll n;
    cin >> n;
    vector<ll> a(n),b(n);
    ll sum_a=0,sum_b=0,sum_c=0;
    rep(i,n){
        cin >> a[i];
        sum_a+=a[i];
    }
    rep(i,n){
        cin >> b[i];
        sum_b+=b[i];
    }
    if(n==2){
        ll d0=a[0]-b[0];
        ll d1=b[1]-a[1];
        if(d0==d1){
            cout << abs(d0) << endl;
        }
        else{
            cout << -1 << endl;
        }
        return 0;
    }
    ll cnt=(sum_a-sum_b)/(n-2); //操作回数の和
    bool ok=true;
    rep(i,n){
        ll x=cnt+b[i]-a[i];
        if(x%2==1  || x<0){
            ok=false;
            break;
        }
        else{
            sum_c+=(x/2);
        }
        
    }
    if(sum_c!=cnt) ok=false;
    if(ok) cout << cnt << endl;
    else cout << -1 << endl;
    return 0;
}