module Main where

import Numeric
import Data.Functor

main :: IO ()
main =  do
  { [n] <- getDoubles
  ; if n == 0 then done
    else do
      { si  <- getDoubles
      ; let m = sum si / n
      ; let s2 = (sum $ map ((^2) . (subtract m)) si) / n
      ; let s  = sqrt s2
      ; putStrLn (showFFloat Nothing s "")
      ; main
      }
  }

done :: IO ()
done = return ()

getDoubles :: IO [Double]
getDoubles = map read . words <$> getLine