import Control.Applicative
import Control.Monad
import qualified Data.ByteString.Char8 as B
import Data.Maybe (fromJust)
import Text.Printf
import Debug.Trace

readInts :: B.ByteString -> [Int]
readInts = map (fst . fromJust . B.readInt) . B.words

getInts :: IO [Int]
getInts = liftM readInts B.getLine

getDoubles :: IO [Double]
getDoubles = map fromIntegral <$> getInts

main = do
  [vl,vr] <- getDoubles
  [d] <- getDoubles
  [w] <- getDoubles
  printf "%10f\n" $ d / (vl+vr) * w