import Text.Printf
import Control.Monad
avg list = sum list / (fromIntegral (length list) :: Double) 
main = do
  n <- readLn
  when (n /= 0) $ do
    s <- return . map (\x -> read x :: Double) . words =<< getLine
    let m = avg s
    putStrLn $ printf "%.08f" $ sqrt $ (/) (sum $ map (\x -> (x - m)^2) s) n
    main