using System;
using System.IO;
using System.Text.RegularExpressions;

namespace YukiCoder.No236 {
    class CoffeeTea {
        public static void Main() {
            var scn = new Scanner(Console.In);
            int[] a = scn.NextIntAry();
            int A = a[0], B = a[1], X = a[2], Y = a[3];

            double productMax = 0;
            if (A*Y >= B*X) { // coffee <= tea
                productMax = X * (A + B) / (double)A;
            } else {// coffee > tea
                productMax =  Y * (B + A) / (double)B;
            }

            Console.WriteLine("{0:F12}", productMax);
        }
    }

    public class Scanner {
        private TextReader tr;

        public Scanner(TextReader tr) {
            this.tr = tr;
        }

        public Scanner(string filePath) {
            this.tr = new StreamReader(filePath);
        }

        private string readLine() {
            return Regex.Replace(tr.ReadLine(), @"\s+", " ").Trim();
        }

        public string NextStr() {
            return readLine();
        }

        public string[] NextStrAry() {
            return readLine().Split(' ');
        }

        public int NextInt() {
            return int.Parse(readLine());
        }

        public int[] NextIntAry() {
            return Array.ConvertAll(readLine().Split(' '), int.Parse);
        }
    }
}