import Control.Applicative
import Control.Monad
import Text.Printf

var :: Double -> Double -> Double
var s m = (s - m) * (s - m)

solver :: [Double] -> Int -> Double
solver scores n = sqrt $ sum (map (var mean) scores) / fromIntegral n
  where mean = sum scores / fromIntegral n

main :: IO()
main = do
  n <- (read :: String -> Int) <$> getLine
  unless (n == 0) $ do
    scores <- map (read :: String -> Double) . words <$> getLine
    printf "%.8f\n" (solver scores n)
    main