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);
}
}
}