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

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            double[] x = Console.ReadLine().Split().Select(double.Parse).ToArray();
            Console.WriteLine(x[0] * x[3] > x[1] * x[2] ? x[2] + x[2] * x[1] / x[0] : x[3] + x[3] * x[0] / x[1]);
        }
    }
}