import Text.Printf

main = interact $ show' . solve . read'
  where
    show' = unlines . map (printf "%.9f")
    solve [] = []
    solve (x:y:xs) = (solveRow (x ++ y)):(solve xs)
    solveRow (n:xs) = sqrt $ sigma / n
      where
        sigma = sum [(x - avg)**2 | x <- xs]
        avg = (sum xs) / n
    read' = map (map read . words) . init . lines :: String -> [[Double]]

