import Control.Monad
import Control.Applicative
import Data.Functor
import Data.List
import Data.Char

stdev n s = sqrt . (/n) . sum . map ((**2) . subtract (sum s / n)) $ s

main = do
    n <- readLn
    when (n/=0) $ stdev n <$> (map read . words <$> getLine) >>= print >> main