#pragma GCC optimize("Ofast")
#include<iostream>
#include<stdio.h>
#include<algorithm>
#include<vector>
#include<string.h>
#include<math.h>
#include<map>
#include<iomanip>
#include<queue>

const long long INF_L = 1e17+7;
const long long INF_I = 1e9+7;
const long long MOD = 1e9+7;
const double EPS = 1e-8;
const double PI=acos(-1);

using namespace std;

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	
	int n;
	cin >> n;
	vector<int> a(n);
	vector<int> b(n);
	long long sum_a=0;
	for(int i=0;i<n;i++){
		cin >> a[i];
		sum_a+=a[i];
	}
	long long sum_b=0;
	for(int i=0;i<n;i++){
		cin >> b[i];
		sum_b+=b[i];
	}
	
	//cout << sum_a << endl;
	//cout << sum_b << endl;
	
	long long sum_d=sum_a-sum_b;
	if((sum_d%(n-2)==0) && (sum_d>0)){
		cout << sum_d/(n-2) << endl;
	}else{
		cout << -1 << endl;
	}
	return 0;
}