import Numeric

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

showF f = showFFloat Nothing f ""
readNums = fmap (map read . words) getLine

main = do
  n <- readLn
  if n == 0 then return ()
  else do
   ss <- readNums
   putStrLn $ showF $ stddiv ss
   main