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

namespace YukiCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var v = Console.ReadLine().Split().Select(int.Parse).ToArray();
            var A = (double)v[0];
            var B = (double)v[1];
            var X = (double)v[2];
            var Y = (double)v[3];
            var z = B * X < A * Y ? X + X * B / A : Y + Y * A / B;
            Console.WriteLine(z);
            Console.ReadLine();
        }
    }
}