module Main where
--import Debug.Trace
import Data.List
import Data.Char
import Data.Array
import Data.Maybe
import Data.Ord
import Control.Monad

solve :: [(Int, [Double])] -> [Double]
solve [] = []
solve ((n,x):xs)= sd 0 0 x : solve xs where
    sd x1 x2 [] = sqrt (x2/n' - (x1/n')^2)
    sd x1 x2 (d:ds) = sd (x1+d) (x2+d*d) ds
    n' = realToFrac n 

readLine:: IO [Double]
readLine = fmap (map read . words) getLine

readUntil :: (Int -> Bool) -> IO [(Int, [Double])]
readUntil eof = iter where
    iter = do
        n <- readLn
        if eof n then return []
                 else do
                    a <- readLine
                    fmap ((n, a):) iter
            
eof :: Int -> Bool
eof s = s == 0

main :: IO() 
main = do
    l   <- readUntil eof
    mapM_ print (solve l)

