#include <iostream>
#include <vector>

using namespace std;
int main(){
  int n;cin>>n;
  vector<int> A(n), B(n);
  for(int i = 0; n > i; i++){
    cin>>A[i];
  }
  for(int i = 0; n > i; i++){
    cin>>B[i];
  }
  if(n == 2){
    if(A[0]+A[1] == B[0]+B[1]){
      cout << abs(A[0]-B[0]) << endl;
    }else{
      cout << -1 << endl;
    }
  }else{
    int dif = 0;
    for(int i = 0; n > i; i++){
      dif += A[i]-B[i];
    }
    if(dif < 0 || dif%(n-2)){
      cout << -1 << endl;
      return 0;
    }
    int c = dif/(n-2);
    
    int nw = 0;
    for(int i = 0; n > i; i++){
      int mn = A[i]-c;
      if((B[i]-mn)%2){
        cout << -1 << endl;
        return 0;
      }
      nw += (B[i]-mn)/2;
    }
    if(nw == c){
      cout << c << endl;
    }else{
      cout << -1 << endl;
    }
  }
}