object Main {
    val Array(vl, vr) = io.StdIn.readLine.split(" ").map(_.toDouble)
    val d = io.StdIn.readLine.toDouble
    val w = io.StdIn.readLine.toDouble
    def main(args: Array[String]) = {
        println(d / (vl + vr) * w)
    }
}