import java.util.*;

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