#include <cstdio>
#include <iostream>
#include <string>
#include <sstream>
#include <stack>
#include <algorithm>
#include <cmath>
#include <queue>
#include <map>
#include <set>
#include <cstdlib>
#include <bitset>
#include <tuple>
#include <assert.h>
#include <deque>
#include <bitset>
#include <iomanip>
#include <limits>
#include <chrono>
#include <random>
#include <array>
#include <unordered_map>
#include <functional>
#include <complex>
#include <numeric>
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
//constexpr long long MAX = 5100000;
constexpr long long INF = 1LL << 60;
constexpr int inf = 1000000007;
//constexpr long long mod = 1000000007LL;
constexpr long long mod = 998244353LL;
const long double PI = acos((long double)(-1));

using namespace std;
typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;

void fail() {
    puts("-1");
    exit(0);
}
int main()
{
    /*
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    */

    int n; scanf("%d", &n);
    ll suma = 0, sumb = 0;
    vector<ll> a(n); for (int i = 0; i < n; i++) scanf("%lld", &a[i]), suma += a[i];
    vector<ll> b(n); for (int i = 0; i < n; i++) scanf("%lld", &b[i]), sumb += b[i];
    if (suma < sumb) fail();
    
    if (n == 2) {
        if (suma != sumb) fail();
        printf("%lld\n", llabs(a[0] - b[0]));
        return 0;
    }
    ll sa = suma - sumb;
    if (sa % (n - 2) != 0) fail();
    ll cnt = sa / (n - 2);
    ll res = cnt;
    for (int i = 0; i < n; i++) {
        a[i] -= cnt;
    }
    for (int i = 0; i < n; i++) {
        if (a[i] > b[i]) fail();
        if ((b[i] - a[i]) % 2 == 1) fail();
        ll t = (b[i] - a[i]) / 2;
        if (cnt < t) fail();
        cnt -= t;
    }
    cout << res << endl;
    return 0;
}