main = do
  s <- getLine
  let n = read s :: Int
  if n == 0 then
    return ()
  else do
    getLine >>= (putStrLn . show . stddev . map read . words)
    main

stddev :: [Int] -> Double
stddev xs = let n=fromIntegral(length xs)
                ave = (fromIntegral (sum xs)) / n in
  sqrt ((sum $ map ( (^ 2).(flip (-) ave).fromIntegral) xs) / n)