import Numeric
stddev ns =
  sqrt $ ((sum [(s-m)^2 | s <- ns]) / n)
  where m = sum ns / n
        n = fromIntegral $ length ns

main = do
  n <- readLn :: IO Int
  if n == 0 then return ()
  else do
    putStrLn =<< fmap (show . stddev . (map read . words)) getLine
    main