using System;
using System.Linq;
class Program {
    static void Main() {
        double[] line = Console.ReadLine().Split().Select(double.Parse).ToArray();
        double ans, a = line[0], b = line[1], x = line[2], y = line[3];
        if (0 < a * y - b * x) {
            ans = (a + b) * x / a;
        } else {
            ans = (a + b) * y / b;
        }

        Console.WriteLine(ans);
    }
}