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

typedef long long ll;
#define REP(i,n) for(int i=0,_n=(int)(n);i<_n;++i)
#define ALL(v) (v).begin(),(v).end()
#define CLR(t,v) memset(t,(v),sizeof(t))
template<class T1,class T2>ostream& operator<<(ostream& os,const pair<T1,T2>&a){return os<<"("<<a.first<<","<<a.second<< ")";}
template<class T>void pv(T a,T b){for(T i=a;i!=b;++i)cout<<(*i)<<" ";cout<<endl;}
template<class T>void chmin(T&a,const T&b){if(a>b)a=b;}
template<class T>void chmax(T&a,const T&b){if(a<b)a=b;}

ll nextLong() { ll x; scanf("%lld", &x); return x;}

int main2() {
  int N = nextLong();
  vector<ll> A(N), B(N);
  REP(i, N) A[i] = nextLong();
  REP(i, N) B[i] = nextLong();

  ll sumA = accumulate(ALL(A), 0LL);
  ll sumB = accumulate(ALL(B), 0LL);


  if (N == 2) {
    if (sumA != sumB) {
      cout << -1 << endl;
    } else {
      bool ng = false;
      ll kk = 0;
      REP(i, N) {
        int d = abs(A[i] - B[i]);
        if (d % 2) ng = true;
        kk += d / 2;
      }
      if (ng) {
        cout << -1 << endl;
      } else {
        cout << kk << endl;
      }
    }
    return 0;
  }


  if ((sumA - sumB) % (N - 2) != 0) {
    cout << -1 << endl;
    return 0;
  }

  bool ng = false;
  ll k = (sumA - sumB) / (N-2);

  ll kk = 0;
  REP(i, N) {
    int d = B[i] - (A[i] - k);
    if (d < 0 || d % 2) { ng = true; }
    kk += d/2;
  }

  ng = ng && (kk == k);

  if (ng)
    cout << -1 << endl;
  else
    cout << k << endl;
  return 0;
}

int main() {

#ifdef LOCAL
  for (;!cin.eof();cin>>ws)
#endif
    main2();
  return 0;
}