main = interact $ unlines . map (show . itp1_10_c) . read' . lines
 where read' xs = case xs of {["0"] -> []; (n:ss:xs') -> (read n, map read (words ss)) : read' xs'} 

itp1_10_c (n,ss) = sqrt $ sum (map (\s -> (s - med ss)^2) ss) / fromIntegral n
 where med ss = sum ss / fromIntegral n