using System;

namespace Yukicoder
{
    public class Program
    {
        public static void Main()
        {
            var v = Console.ReadLine().Split();
            double vL = int.Parse(v[0]);
            double vR = int.Parse(v[1]);
            double d = int.Parse(Console.ReadLine());
            double w = int.Parse(Console.ReadLine());
            bool isRight = true;
            double sum = 0;
            while (d > double.Epsilon)
            {
                double t = isRight ? d / (vR + w) : d / (vL + w);
                if (t < double.Epsilon)
                    break;
                sum += w * t;
                isRight = !isRight;
                d = d - (vL + vR) * t;
            }
            Console.WriteLine(sum);
        }
    }
}