import Text.Printf

sd :: [Double] -> Double
sd nums = abs $ sqrt sigma2
  where
    n      = fromIntegral $ length nums :: Double
    ave    = (sum nums) / n
    sigma2 = (sum $ map (\s -> (s - ave)^^2) nums) / n

main :: IO ()
main = do
    n <- getLine
    if n == "0"
        then
            return ()
        else do
            nums <- getLine >>= return . map (\x -> read x :: Double) . words
            printf "%.5f\n" $ sd nums
            main

