fn getline() -> String{
	let mut __ret=String::new();
	std::io::stdin().read_line(&mut __ret).ok();
	return __ret;
}

fn main(){
	let s=getline();
	let s:Vec<_>=s.trim().split(' ').collect();
	let N:i32=s[0].parse().unwrap();
	let M:i32=s[1].parse().unwrap();
    let s=getline();
    let A:Vec<_>=s.trim().split(' ').collect();
    let s=getline();
    let B:Vec<_>=s.trim().split(' ').collect();
	for i in 0..N*M+1 {
        let X:i32=A[(i % N) as usize].parse().unwrap();
        let Y:i32=B[(i % M) as usize].parse().unwrap();
        if X == Y {
            print!("{}", i+1);
            break;
        }
        if i == N*M {
            print!("{}", -1);
            break;
        }
    }
}