using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    public void Proc()
    {
        Reader.IsDebug = false;
        double[] inpt = Reader.ReadLine().Split(' ').Select(a=>double.Parse(a)).ToArray();
        double hi1 = inpt[0];
        double hi2 = inpt[1];
        double val1 = inpt[2];
        double val2 = inpt[3];
        double ans = 0;
        if(hi1 == hi2) {
            ans = Math.Min(val1, val2) * 2;
        } else
        {
            double tmp = val1 * hi2 / hi1;
            if(tmp > val2) {
                ans = val2 + (val2 * hi1 / hi2);
            } else
            {
                ans = val1 + tmp;
            }
        }
        Console.WriteLine(ans);

    }
    
    
    public class Reader
    {
        public static bool IsDebug = true;
        private static String PlainInput = @"

4 6 150 200
 
";
        private static System.IO.StringReader Sr = null;
        public static string ReadLine()
        {
            if (IsDebug)
            {
                if (Sr == null)
                {
                    Sr = new System.IO.StringReader(PlainInput.Trim());
                }
                return Sr.ReadLine();
            }
            else
            {
                return Console.ReadLine();
            }
        }
        public static int[] GetInt(char delimiter = ' ', bool trim = false)
        {
            string inptStr = ReadLine();
            if (trim)
            {
                inptStr = inptStr.Trim();
            }
            string[] inpt = inptStr.Split(delimiter);
            int[] ret = new int[inpt.Length];
            for (int i = 0; i < inpt.Length; i++)
            {
                ret[i] = int.Parse(inpt[i]);
            }
            return ret;
        }
    }
    static void Main()
    {
        Program prg = new Program();
        prg.Proc();
    }
}