using System;

public class Hello
{
    public static void Main()
    {
        string[] line = Console.ReadLine().Trim().Split(' ');
        var a = double.Parse(line[0]);
        var b = double.Parse(line[1]);
        var x = double.Parse(line[2]);
        var y = double.Parse(line[3]);
        var nx = a * y / b;
        if (x >= nx) { Console.WriteLine(nx + y); goto end; }
        var ny = b * x / a;
        Console.WriteLine(x + ny);
        end:;
    }
}