#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
signed main() { 
  ios::sync_with_stdio(false); cin.tie(0);
  int n;
  cin >> n;
  vector<long long> a(n), b(n);
  long long sum_a = 0, sum_b = 0;
  for (auto& x : a) {
    cin >> x;
    sum_a += x;
  }
  for (auto& x : b) {
    cin >> x;
    sum_b += x;
  }
  if (n >= 3) {
    if (sum_a < sum_b || (sum_a - sum_b) % (n - 2) != 0) {
      cout << -1 << endl;
      return 0;
    }
    long long opr = (sum_a - sum_b) / (n - 2);
    for (auto& x : a) {
      x -= opr;
    }
    long long cnt = 0;
    for (int i = 0; i < n; i++) {
      if (a[i] > b[i] || (b[i] - a[i]) % 2 != 0) {
        cout << -1 << endl;
        return 0;
      }
      cnt += (b[i] - a[i]) / 2;
    }
    cout << (opr == cnt ? opr : -1) << endl;
  } else {
    cout << ((a[0] - b[0]) == (b[1] - a[1]) ? abs(a[0] - b[0]) : -1) << endl;
  }
  return 0;
}