import Text.Printf

main = do
    n <- getLine
    if n == "0"
        then return ()
        else do
            solve
            main

solve = do
    ss <- getLine
    let ns = map (\x -> read x :: Double) $ words ss
    printf "%.8f\n" (sd ns)

variance l = (sum $ map (\x -> (x- (avg l))^2) l) / (fromIntegral $ length l)
avg l = (sum l) / (fromIntegral $ length l)

sd l = sqrt $ variance l
