package no236;

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double a = sc.nextDouble();
		double b = sc.nextDouble();
		double x = sc.nextDouble();
		double y = sc.nextDouble();
		System.out.println(Math.min(x/a, y/b) * (a + b));
	}

}