/* -*- coding: utf-8 -*-
 *
 * 1120.cc:  No.1120 Strange Teacher - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 100000;

/* typedef */

typedef long long ll;

/* global variables */

int as[MAX_N], bs[MAX_N];

/* subroutines */

/* main */

int main() {
  int n;
  scanf("%d", &n);

  ll asum = 0, bsum = 0, psum = 0;
  for (int i = 0; i < n; i++)
    scanf("%d", as + i), asum += as[i];
  for (int i = 0; i < n; i++) {
    scanf("%d", bs + i), bsum += bs[i];
    if (as[i] < bs[i]) psum += bs[i] - as[i];
  }

  int d = n - 2;
  ll f = asum - bsum;
  //printf("d=%d, f=%lld\n", d, f);

  if (d == 0)
    printf("%lld\n", (f == 0) ? psum : -1LL);
  else
    printf("%lld\n", (f >= 0 && f % d == 0 && psum <= f / d) ? f / d : -1LL);
  return 0;
}