#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;
const long long INF = 1001001001;
const long long MOD = 1000000007;
const double EPS = 1e-10;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    ll n;
    cin>>n;
    ll a[n],b[n],sum=0,sum2=0,ans=0;
    for(int i=0;i<n;i++)cin>>a[i];
    if(n==2){
        for(int i=0;i<n;i++)cin>>b[i];
        if(a[0]+a[1]==b[0]+b[1])cout<<abs(a[0]-b[0])<<endl;
        else cout<<-1<<endl;
        return 0;
    }
    for(int i=0;i<n;i++){
        cin>>b[i];
        ll c=a[i]-b[i];
        sum+=c;
        sum2+=c;
        ans+=sum/(n-2);
        sum%=(n-2);
    }
    if(sum==0&&sum2<=(n-2))cout<<ans<<endl;
    else cout<<-1<<endl;
}