fn egcd(a: i64, b: i64) -> (i64, i64) {
	if b == 0 {
		return (1, 0);
	}
	let (x, y) = egcd(b, a % b);
	(y, x - a / b * y)
}

fn main() {
	let mut s = String::new();
	std::io::stdin().read_line(&mut s).ok();
	let n: Vec<i64> = s.split_whitespace().flat_map(str::parse).collect();
	let g = egcd(n[0], n[1]);
	let l = n[0] * n[1];
	println!("{}", ((g.0 * n[0] * n[3] + g.1 * n[1] * n[2]) % l + l) % l);
}