#include <bits/stdc++.h>
using namespace std;

int main()
{
	int64_t n;
	cin >> n;
	vector<int64_t> a(n);
	vector<int64_t> b(n);
	int64_t as = 0;
	int64_t bs = 0;
	for(int64_t i = 0; i < n; i++)
	{
		cin >> a[i];
		as += a[i];
	}
	for(int64_t i = 0; i < n; i++)
	{
		cin >> b[i];
		bs += b[i];
	}
	
	if(as - bs < 0)
	{
		cout << -1 << endl;
		return 0;
	}
	if(n == 2)
	{
		if(as != bs) cout << -1 << endl;
		else cout << abs(a[0] - b[0]) << endl;
		return 0;
	}
	
	if((as - bs) % (n - 2) != 0)
	{
		cout << -1 << endl;
		return 0;
	}
	
	int64_t k = (as - bs) / (n - 2);
	for(int64_t i = 0; i < n; i++) a[i] -= k;
	int64_t cnt = 0;
	for(int64_t i = 0; i < n; i++)
	{
		if(a[i] > b[i])
		{
			cout << -1 << endl;
			return 0;
		}
		if((b[i] - a[i]) % 2 != 0)
		{
			cout << -1 << endl;
			return 0;
		}
		cnt += (b[i] - a[i]) / 2;
	}
	if(k == cnt) cout << k << endl;
	else cout << -1 << endl;
	return 0;
}