import Data.Ratio
import Text.Printf
import Data.Fixed

apply n f x = foldr ($) x (replicate n f)

main = do
 [xa,ya] <- map read . words <$> getLine :: IO [Double]
 [xb,yb] <- map read . words <$> getLine :: IO [Double]
 print (saitama xa ya xb yb) 

saitama xa ya xb yb
 | ya > yb = snd $ apply 100 (triSearch (euc xa ya xb yb)) (ya,yb)
 | otherwise = snd $ apply 100 (triSearch (euc xb yb xa ya)) (yb,ya)

triSearch f (lo,hi)
 | f md1 < f md2 = (lo,md2) 
 | otherwise = (md1,hi)
 where
  md1 = lo + (hi-lo)/3
  md2 = lo + (2*(hi-lo))/3

euc xa ya xb yb yp = dist (0,yp) (xa,ya) + dist (0,yp) (xb,yb)
 where dist (p1,q1) (p2,q2) = sqrt $ (p1-p2)^2 + (q1-q2)^2