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>();
    let f1 = (0..n).all(|i| (a[i] - b[i]).abs() % 2 == (a[0] - b[0]).abs() % 2);
    let f2 = a_sum >= b_sum;
    let f3 = (a_sum - b_sum) % (n - 2) as i64 == 0;
    let f4 = (0..n).all(|i| (a[i] - b[i]).abs() <= (a_sum - b_sum) / (n - 2) as i64);
    let ans = if f1 && f2 && f3 && f4 {
        (a_sum - b_sum) / (n - 2) as i64
    } else {
        -1
    };

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