import Numeric

mean :: Floating a => [a] -> a
mean xs = sum xs / (fromIntegral $ length xs)

var :: Floating a => [a] -> a
var xs = mean [x ** 2| x <- xs] - mean xs ** 2

stddev :: Floating a => [a] -> a
stddev = sqrt . var

main :: IO ()
main = do
  n <- readLn
  if n == 0 then return () else do
    s <- fmap (map read . words) getLine
    putStrLn $ showFFloat Nothing (stddev s) ""
    main