import Control.Applicative
import Control.Monad
import Data.Array
import Data.Array.ST
import Data.Char
import Data.List
import qualified Data.Map as M
import qualified Data.Set as S
import Text.Printf

readInts :: IO [Int]
readInts = map read . words <$> getLine

main :: IO ()
main = do
  n <- readLn
  when (n /= 0) $ do
    ss <- map read . words <$> getLine
    print $ sd n ss
    main

sd :: Int -> [Double] -> Double
sd n ss = sqrt (sum [ (s - m)^2 | s <- ss ] / fromIntegral n)
 where
  m = mean n ss

mean :: Int -> [Double] -> Double
mean n ss = sum ss / fromIntegral n

