use proconio::input;

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

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

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

    let sum_a = a.iter().sum::<i64>();
    let sum_b = b.iter().sum::<i64>();
    if sum_a < sum_b || (sum_a - sum_b) % (n - 2) as i64 != 0 {
        println!("-1");
        return;
    }

    let m = (sum_a - sum_b) / (n - 2) as i64;
    let mut cnt = 0;
    for i in 0..n {
        if a[i] - m > b[i] || (b[i] - (a[i] - m)) % 2 != 0 {
            println!("-1");
            return;
        }

        cnt += (b[i] - (a[i] - m)) / 2;
    }
    if cnt != m {
        println!("-1");
        return;
    }

    let ans = m;
    println!("{}", ans);
}