fn main() {
    let n: usize = {
        let mut buf = String::new();
        std::io::stdin().read_line(&mut buf).unwrap();
        buf.trim_end().parse().unwrap()
    };
    let a: Vec<i64> = {
        let mut buf = String::new();
        std::io::stdin().read_line(&mut buf).unwrap();
        let iter = buf.split_whitespace();
        iter.map(|x| x.parse().unwrap()).collect()
    };
    let b: Vec<i64> = {
        let mut buf = String::new();
        std::io::stdin().read_line(&mut buf).unwrap();
        let iter = buf.split_whitespace();
        iter.map(|x| x.parse().unwrap()).collect()
    };

    let sum_a = a.iter().fold(0, |acc, x| acc + x);
    let sum_b = b.iter().fold(0, |acc, x| acc + x);

    if n == 2 {
        if sum_a == sum_b {
            println!("{}", (a[0] - b[0]).abs());
        } else {
            println!("-1");
        }
        return;
    }

    if sum_a < sum_b || (sum_a - sum_b) % (n - 2) as i64 > 0 {
        println!("-1");
        return;
    }

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