import Control.Monad
import Text.Printf

main :: IO ()
main = do
    n <- readLn
    unless (n == 0) $ do
        ns <- fmap (map read . words) getLine
        printf "%.8f\n" (sd ns)
        main

sd :: [Double] -> Double
sd xs = sqrt v
    where v = sum [(x-m)^2 | x <- xs] / n
          m = sum xs / n
          n = fromIntegral (length xs)
