import Control.Applicative
import Text.Printf

stddev :: Floating a => [a] -> a
stddev ss = sqrt $ (sum [(s - m) ^ 2 | s <- ss]) / n
    where
        n = (fromIntegral . length) ss
        m = (sum ss) / n

main :: IO ()
main = do
    n <- getLine
    if (n == "0")
    then return ()
    else do
       printf "%.8f\n" =<< (stddev . map (read :: String -> Double) . words) <$> getLine
       main