#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]; for(int i=0;i<n;i++)cin>>a[i]; for(int i=0;i<n;i++)cin>>b[i]; ll diff=0; for(int i=0;i<n;i++)diff+=a[i]-b[i]; if(n==2){ if(a[0]-b[0]==b[1]-a[1])cout<<abs(a[0]-b[0])<<endl; else cout<<-1<<endl; return 0; } if(diff%(n-2)!=0){ cout<<-1<<endl; return 0; } ll cnt=diff/(n-2); ll pls=0; for(int i=0;i<n;i++){ ll d=a[i]-cnt; ll e=b[i]-d; if(e<0){ cout<<-1<<endl; return 0; } pls+=e/2; } if(pls==cnt)cout<<cnt<<endl; else cout<<-1<<endl; }