//https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8 より
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}

//

fn run() {
    input! {
        n: usize,
        a: [i64; n],
        b: [i64; n],
    }
    let sa = a.iter().sum::<i64>();
    let sb = b.iter().sum::<i64>();
    if n == 2 {
        if sa != sb {
            println!("-1");
        } else {
            println!("{}", (a[0] - b[0]).abs());
        }
        return;
    }
    let sub = (n - 1 - 1) as i64;
    if sa < sb || (sa - sb) % sub != 0 {
        println!("-1");
        return;
    }
    let d = (sa - sb) / sub;
    let mut free = d;
    for (a, b) in a.iter().zip(b.iter()) {
        let diff = *a - *b;
        if (d - diff) % 2 != 0 || diff.abs() > d {
            println!("-1");
            return;
        }
        free -= (d - diff) / 2;
    }
    if free == 0 {
        println!("{}", d);
    } else {
        println!("-1");
    }
}

fn main() {
    run();
}