use std::io::Read;

fn main() {
	let mut s = String::new();
	std::io::stdin().read_to_string(&mut s).ok();
	let l: Vec<_> = s.lines().collect();
	let (n, a, b): (Vec<usize>, _, _) = (
		l[0].split(' ').flat_map(str::parse).collect(),
		l[1].split(' ').flat_map(str::parse::<u64>),
		l[2].split(' ').flat_map(str::parse::<u64>),
	);
	let p = a
		.cycle()
		.zip(b.cycle())
		.take(n[0] * n[1])
		.position(|(a, b)| a == b)
		.map_or(-1, |p| 1 + p as i64);
	println!("{p}")
}