import Control.Monad
import Data.List

main = do
 [vl,vr,d,w] <- map read . words <$> getContents
 print (shuttle vl vr d w)

shuttle vl vr d w = sum $ take 100 $ unfoldr tofrom d
 where tofrom d' = let db = d'*(w/(w+vr)) + (d'-d'*(w/(w+vr)))*(w/(w+vl)) in Just (db,d'-db*((vl+vr)/w))