#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <queue>
#include <cstdio>
#include <ctime>
#include <assert.h>
#include <chrono>
#include <random>
#include <numeric>
#include <set>
#include <deque>
using namespace std;
typedef long long int ll;
typedef unsigned long long ull;


signed main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n; cin >> n;
    vector<ll> a(n),b(n);
    ll sum=0,sum2=0;
    for(int i=0;i<n;i++){
        cin >> a[i];
        sum+=a[i];
    }
    for(int i=0;i<n;i++){
        cin >> b[i];
        sum2+=b[i];
    }
    if(n==2){
        if(a[0]+a[1]==b[0]+b[1]){
            printf("%lld\n",abs(a[0]-b[0]));
        }
        else{
            printf("-1\n");
        }
        return 0;
    }
    if(sum2>sum||(sum-sum2)%(n-2)){
        printf("-1\n");
        return 0;
    }
    ll k=(sum-sum2)/(n-2);
    for(int i=0;i<n;i++){
        a[i]-=k;
    }
    ll p=0;
    bool ok=1;
    for(int i=0;i<n;i++){
        if(a[i]>b[i])ok=0;
        if((b[i]-a[i])%2)ok=0;
        p+=(b[i]-a[i])/2;
    }
    if(ok&&p==k){
        printf("%lld\n",k);
    }
    else{
        printf("-1\n");
    }
}