fn read() -> Vec<usize> {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    let mut itr = s.trim().split_whitespace();
    
    itr.map(|x| x.parse::<usize>().unwrap()).collect()
}

fn main() {
    let nm = read();
    let a = read();
    let b= read();

    for i in 0..nm[0] * nm[1] {
        if a[i % nm[0]] == b[i % nm[1]] {
            println!("{}", i + 1);
            return
        }
    }
    println!("{}", -1);
}