import std.stdio, std.array, std.string, std.conv, std.algorithm;
import std.typecons, std.range, std.random, std.math, std.container;
import std.numeric, std.bigint, core.bitop, core.stdc.stdlib, std.datetime;

void main() {
    auto N = readln.chomp.to!int;
    auto A = readln.split.map!(to!long).array;
    auto B = readln.split.map!(to!long).array;

    auto sa = A.sum;
    auto sb = B.sum;

    if (N == 2) {
        if (sa != sb) {
            writeln(-1);
        } else {
            writeln(abs(A.front - B.front));
        }
        return;
    }

    if (sa < sb) {
        writeln(-1);
        return;
    }

    if ((sa - sb) % (N - 2) != 0) {
        writeln(-1);
        return;
    }

    auto cnt = (sa - sb) / (N - 2);

    A[] -= cnt;

    long cnt2 = 0;

    foreach (i, a; A) {
        if (A[i] > B[i] || (B[i] - A[i]) % 2 != 0) {
            writeln(-1);
            return;
        }
        cnt2 += (B[i] - A[i]) / 2;
    }


    writeln(cnt == cnt2 ? cnt : -1);
}