import Control.Applicative ((<$>), (<*>))

main :: IO ()
main = do
  solve <$> getl read <*> getl (map read . words) >>= print

solve :: Int -> [Int] -> Double
solve c [ri, ro] = let rc = fromIntegral (ro - ri) / 2.0 :: Double
                       rr = fromIntegral (ro + ri) / 2.0 :: Double
                   in 2.0 * (acos (-1)) ** 2.0 * rr * rc ** 2.0 * fromIntegral c

getl :: (String -> a) -> IO a
getl f = f <$> getLine