#include<iostream>
#include <cstring>
#include<string>
#include<algorithm>
#include<vector>
#include<iomanip>
#include<math.h>
#include<complex>
#include<queue>
#include<deque>
#include<stack>
#include<map>
#include<set>
#include<bitset>
#include<functional>
#include<assert.h>
#include<numeric>
using namespace std;
#define REP(i,m,n) for(int i=(int)(m) ; i < (int) (n) ; ++i )
#define rep(i,n) REP(i,0,n)
using ll = long long;
typedef pair<int,int> pint;
typedef pair<ll,int> pli;
const int inf=1e9+7;
const ll longinf=1LL<<60 ;
const ll mod=1e9+7 ;

  
  
   

int main(){
  int n; cin >> n; ll a[n], b[n], sa[n];
  rep(i, n){
    cin >> a[i];
  }
  rep(i, n){
    cin >> b[i];
  }
  ll sum = 0;
  rep(i, n){
    sa[i] = a[i]-b[i]; sum+=sa[i];
  }
  if(n==2){
    if(sum!=0) cout << -1 << endl;
    else cout << sa[0] << endl;
    return 0;
  }
  bool can = true;
  if(sum%(n-2)!=0) can = false;
  if(sum<0) can = false;
  //cout << can << endl;
  rep(i, n-1){
    if(abs(sa[i])%2!=abs(sa[i+1])%2) can=false;
  }
  sort(sa, sa+n, greater<>()); ll kai[n]; kai[0] = 0; ll k = 0;
  rep(i, n-1){
    kai[i+1] = kai[i]+(sa[i]-sa[i+1])/2; k+=kai[i+1]; //cout << kai[i+1] << endl;
  }
  if(k>sum/(n-2)) can=false;
  if(can) cout << sum/(n-2) << endl;
  else cout << -1 << endl;
}