fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let n: usize = n.trim().parse().unwrap();
    let mut a = String::new();
    std::io::stdin().read_line(&mut a).ok();
    let a: Vec<isize> = a.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let mut b = String::new();
    std::io::stdin().read_line(&mut b).ok();
    let b: Vec<isize> = b.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();

    let diffs: Vec<isize> = b.iter().zip(a.iter())
        .map(|ba| *ba.0 - *ba.1)
        .collect();
    let count: isize = -1isize * diffs.iter().sum::<isize>();
    if (n == 2 && count == 0isize) || (n > 2 && count % (n as isize - 2isize) == 0) {
        let count = if n > 2 { count / (n as isize - 2isize) } else { 0isize } ;
        if n == 2 {
            println!("{}", diffs[0].abs());
        } else {
            let has_irdata = b.iter().zip(a.iter())
                .filter(|ba| (*ba.1 - *ba.0).abs() > count || (*ba.0 -  *ba.1).abs() % 2 != count % 2)
                .count() > 0;
            let actualcount: isize = b.iter().zip(a.iter())
                .map(|ba| *ba.0 - (*ba.1 - count))
                .map(|i| i / 2)
                .sum()
            ;
            println!("{}", if has_irdata || actualcount != count { -1 } else { count });
        }
    } else {
        println!("-1");
    }
}