fn main() {
	let mut s = String::new();
	std::io::stdin().read_line(&mut s).ok();
	let n: Vec<f64> = s.split_whitespace().flat_map(str::parse).collect();
	println!("{}", (n[2] / n[0]).min(n[3] / n[1]) * (n[0] + n[1]))
}