#include<bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i,n) for(int i=0;i<n;i++)
#define REP(i,n) for(int i=1;i<n;i++)
#define rev(i,n) for(int i=n-1;i>=0;i--)
#define all(v) v.begin(),v.end()
#define P pair<int,int>
#define len(s) (int)s.size()

template<class T> inline bool chmin(T &a, T b){
	if(a>b){a=b;return true;}
	return false;
}
template<class T> inline bool chmax(T &a, T b){
	if(a<b){a=b;return true;}
	return false;
}
constexpr int mod = 998244353;
constexpr int inf = 3e18;

int N,A[100005],B[100005];
signed main(){
	cin>>N;
	int sum1=0,sum2=0;
	rep(i,N){
		cin>>A[i];sum1+=A[i];
	}
	int mx=0;
	rep(i,N){
		cin>>B[i];sum2+=B[i];
		chmax(mx,abs(B[i]-A[i]));
	}
	if(sum1<sum2)cout<<"-1"<<endl;
	else if((sum1-sum2)%(N-2))cout<<"-1\n";
	else if((sum1-sum2)/(N-2)<mx)cout<<"-1\n";
	else cout<<(sum1-sum2)/(N-2)<<endl;
}