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 mut c = vec![0; n];
    for i in 0..n {
        c[i] = a[i] - b[i];
    }
    c.sort();

    let ans = {
        if n == 2 {
            let x = c[1] - c[0];
            if x % 2 == 0 {
                x / 2
            } else {
                -1
            }
        } else {
            if (2..(n - 1)).fold(true, |acc, i| acc && c[i] == c[i + 1]) {
                let x = c[2] - c[1];
                if x % 2 == 0 {
                    let y = (c[2] + c[1]) / 2 - (c[0] - x / 2);
                    if y % 2 == 0 {
                        x / 2 + y / 2
                    } else {
                        -1
                    }
                } else {
                    -1
                }
            } else {
                -1
            }
        }
    };
    println!("{}", ans);
}