main = do
  n <- readLn::IO Int
  if n == 0 then return ()
  else do
    v <- (return . map (read::String->Double) . words) =<< getLine
    print $ stdv v
    main
mean v = (sum v) / ((fromIntegral::Int->Double) (length v))
stdv v = (mean $ map ((**2.0) . subtract (mean v)) v)**0.5
