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

public class Program
{
    public void Proc() {
        Reader.IsDebug = false;
        decimal[] inpt = Reader.ReadLine().Split(' ').Select(a=>decimal.Parse(a)).ToArray();
        this.V1 = inpt[0];
        this.V2 = inpt[1];
        this.D = decimal.Parse(Reader.ReadLine());
        this.W = decimal.Parse(Reader.ReadLine());
        decimal ans = D / (V1 + V2) * W;
        Console.WriteLine(ans);
    }

    private decimal V1;
    private decimal V2;

    private decimal D;
    private decimal W;


    public class Reader {
        public static bool IsDebug = true;
        private static System.IO.StringReader SReader;
        private static string InitText = @"


90 568
5019
870




";
        public static string ReadLine() {
            if(IsDebug) {
                if(SReader == null) {
                    SReader = new System.IO.StringReader(InitText.Trim());
                }
                return SReader.ReadLine();
            } else {
                return Console.ReadLine();
            }
        }

    }
    public static void Main(string[] args)
    {
        Program prg = new Program();
        prg.Proc();
    }
}