import Control.Applicative
import Control.Monad
import Numeric

ssq [x] = x*x
ssq (x:xs) = x*x + ssq xs

var x = ssq x / (fromIntegral.length) x - meanx * meanx where meanx = sum x / (fromIntegral.length) x


main = do
    n <- getLine
    if( n == "0") then return ()
    else do 
      s <- (map read.words) <$> getLine :: IO [Double]
      putStrLn $ showFFloat (Just 7) (sqrt(var s)) ""
      main