import Control.Applicative
import Control.Monad.State

main :: IO ()
main = do
  [vl,vr] <- map read . words <$> getLine :: IO [Double]
  d <- readLn :: IO Double
  w <- readLn :: IO Double
  print $ evalState (simulate vl vr w) (0,d)

simulate :: Double -> Double -> Double -> State (Double, Double) Double
simulate vl vr w = do
  (dist, d) <- get
  let t1 = d/(w+vr)
      t2 = t1+(d-(vl+vr)*t1)/(w+vl)
  put $ (dist+w*t2, d-(vl+vr)*t2)

  if abs d < 0.000001
    then return dist
    else simulate vl vr w