import Control.Applicative
import Control.Monad
import Data.Array
import Data.Array.ST
import Data.Char
import Data.List
import qualified Data.Map as M
import qualified Data.Set as S
import Text.Printf

readInts :: IO [Int]
readInts = map read . words <$> getLine

main :: IO ()
main = do
  [x1,y1,x2,y2] <- map read . words <$> getLine
  print $ sqrt $ (x1 - x2)^2 + (y1 - y2)^2
  
