defmodule Main do
  def main do
    [l, r] =
      IO.read(:line)
      |> String.trim()
      |> String.split()
      |> Enum.map(&String.to_integer/1)

    [d, w] =
      1..2
      |> Enum.map(fn _ -> IO.read(:line) |> String.trim() |> String.to_integer() end)

    solve(l, r, d, w)
    |> IO.puts()
  end

  def solve(l, r, d, w) do
    w * (d / (l + r))
  end
end