using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var a = NList;
        var b = NList;
        WriteLine(Teacher(n, a, b));
    }
    static long Teacher(int n, int[] a, int[] b)
    {
        var asum = 0L;
        var bsum = 0L;
        for (var i = 0; i < n; ++i)
        {
            asum += a[i];
            bsum += b[i];
        }
        if (n == 2)
        {
            if (asum == bsum) return Math.Abs(a[0] - b[0]);
            else return -1;
        }
        var ans = (int)((asum - bsum) / (n - 2));
        if ((asum - bsum) % (n - 2) != 0) return -1;
        for (var i = 0; i < n; ++i)
        {
            a[i] -= ans;
        }
        var add = 0;
        for (var i = 0; i < n; ++i)
        {
            if (b[i] < a[i]) return -1;
            if ((b[i] - a[i]) % 2 == 1) return -1;
            add += (b[i] - a[i]) / 2;
        }
        return add == ans ? ans : -1;
    }
}