#include <iostream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstdlib>
#include <cassert>
#include <vector>
#include <list>
#include <stack>
#include <queue>
#include <deque>
#include <map>
#include <set>
#include <bitset>
#include <string>
#include <algorithm>
#include <utility>
#define llint long long
#define inf 1e18
#define rep(x, s, t) for(llint (x) = (s); (x) < (t); (x)++)
#define Rep(x, s, t) for(llint (x) = (s); (x) <= (t); (x)++)
#define chmin(x, y) (x) = min((x), (y))
#define chmax(x, y) (x) = max((x), (y))

using namespace std;
typedef pair<llint, llint> P;

llint n;
llint a[100005], b[100005];

int main(void)
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	cin >> n;
	for(int i = 1; i <= n; i++) cin >> a[i];
	for(int i = 1; i <= n; i++) cin >> b[i];
	
	llint sum = 0;
	for(int i = 1; i <= n; i++) sum += a[i];
	for(int i = 1; i <= n; i++) sum -= b[i];
	
	if(n == 2){
		if(sum != 0) cout << -1 << endl;
		else cout << abs(a[1]-b[1]) << endl;
		return 0;
	}
	
	if(sum < 0 || sum % (n-2)){
		cout << -1 << endl;
		return 0;
	}
	
	llint k = sum / (n-2);
	llint cnt = 0;
	for(int i = 1; i <= n; i++){
		if(abs(b[i]-a[i]+k) % 2 || (b[i]-a[i]+k) < 0){
			cout << -1 << endl;
			return 0;
		}
		cnt += (b[i]-a[i]+k) / 2;
	}
	if(cnt == k) cout << k << endl;
	else cout << -1 << endl;
	
	return 0;
}