import java.util.*;

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();
    double ans = 0;
    if(X * B <= A * Y) ans = (X * (A + B)) / A;
    if(X * B >= A * Y) ans = Math.max(ans, (Y * (A + B)) / B);
    System.out.println(ans);
  }
}