use proconio::input;

fn main() {
    input! {
        n:usize,
        a:[i64;n],
        b:[i64;n],
    }

    if n == 2 {
        let ans = if a[0] - b[0] + a[1] - b[1] == 0 {
            (a[0] - b[0]).abs()
        } else {
            -1
        };

        println!("{}", ans);
        return;
    }

    let a_sum = a.iter().sum::<i64>();
    let b_sum = b.iter().sum::<i64>();
    if a_sum < b_sum || (a_sum - b_sum) % (n - 2) as i64 != 0 {
        println!("-1");
        return;
    }
    let cnt = (a_sum - b_sum) / (n - 2) as i64;
    let ps = (0..n).map(|i| b[i] - (a[i] - cnt)).collect::<Vec<_>>();

    let f1 = ps.iter().sum::<i64>() == 2 * cnt;
    let f2 = ps.iter().all(|&p| 0 <= p);
    let f3 = ps.iter().all(|&p| p % 2 == 0);
    let ans = if f1 && f2 && f3 { cnt } else { -1 };

    println!("{}", ans);
}