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



int main() {

    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int N;
    cin>>N;
    ll S=0;
    vector<ll> A(N);
    for(int i=0;i<N;i++){
        cin>>A[i];
    }
    for(int i=0;i<N;i++){
        ll a;
        cin>>a;
        A[i]=a-A[i];
        S+=A[i];
    }
    if(N==2){
        cout<<(S==0?abs(A[0]):-1)<<endl;
    }
    else{
        if(S>0||abs(S)%(N-2)!=0){
            cout<<-1<<endl;
            return 0;
        }
        ll D=(abs(S)/(N-2));
        bool OK=1;
        ll K=0;
        for(int i=0;i<N;i++){
            A[i]+=D;
            if(A[i]<0||A[i]%2!=0)OK=0;
            K+=(A[i]/2);
        }
        cout<<(OK&&K==D?D:-1)<<endl;
    }
}