import Control.Applicative

standardDeviation :: [Int] -> Double
standardDeviation s = (sqrt . (/ realToFrac(length s)) . sum . map ((**2) . (`subtract` m) . realToFrac)) s
                    where{
                    m = realToFrac(sum s) / realToFrac(length s)
                    };

main = do{
    l <- lines <$> getContents;
    let{
    l' = [ (standardDeviation . map (read::String->Int) . words) (l!!n) | n<-[1..(length l)-1], n`mod`2==1 ]
    };
    mapM_ putStrLn $ (map show) l'
}