#include <iostream>
#include <vector>
using namespace std;
using ll = long long;
using vi = vector<int>;
void ins() {}
template<class T,class... Rest>void ins(T& v,Rest&... rest){cin>>v;ins(rest...);}

#define rep(i,n) for(int i=0,_i=(n);i<_i;++i)

int main() {
  int N;
  ins(N);

  vi A(N), B(N);
  ll sum = 0, sum2 = 0;
  rep(i, N) {
    cin >> A[i];
    sum += A[i];
  }
  rep(i, N) {
    cin >> B[i];
    sum2 += B[i];
  }
  if (sum < sum2 || (sum - sum2) % (N-2) != 0) {
    cout << -1 << endl;
    return 0;
  }
  int max_diff = -1e9;
  vi diff(N);
  rep(i, N) {
    max_diff = max(max_diff, A[i] - B[i]);
    diff[i] = A[i] - B[i];
  }
  ll sum_diff = 0;
  rep(i, N) {
    diff[i] -= max_diff;
    if (diff[i] % 2 != 0) {
      cout << -1 << endl;
      return 0;
    }
    sum_diff += abs(diff[i]) / 2;
  }
  if (sum_diff == max_diff)
    cout << max_diff << endl;
  else
    cout << -1 << endl;

  return 0;
}

// 全員-1して、ある生徒だけ+2と捉え直す。
// 全員0以下になるまで操作を行う。そこから+2していく