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();
	println!(
		"{}",
		match n[0] - n[1] {
			d if d > 0 => n[1] + d / (n[2] + 1),
			d => n[0] - d / (n[3] + 1),
		}
	)
}