using System;
using System.IO;
using System.Linq;

class Program
{
   
    static void Main()
    {
        double[] input;
        using (var file_str = new StreamReader("input.txt"))
        {
            input = file_str.ReadToEnd().Split().Select(s => Convert.ToDouble(s)).ToArray();
        }

        using (StreamWriter outputFile = new StreamWriter("output.txt"))
        {
            outputFile.WriteLine((int)input[0] / (input[1] + input[2]) * input[3] * 60);
        }

    }
}