import Text.Printf

main :: IO ()
main = getContents >>= mapM_ (printf "%.8f\n" . sd . map read . words) . pick . init . lines
    where pick ss = [s | (i,s) <- zip [1..] ss, even i]

sd :: [Double] -> Double
sd xs = sqrt v
    where v = sum (map ((^2) . subtract m) xs) / n
          m = sum xs / n
          n = fromIntegral (length xs)
