main = do
    str1 <- getLine
    str2 <- getLine
    let
        c = read str1 :: Double
        [r, rl] = map read $ words str2 :: [Double]
        v = pi^2 * (r+rl) * (rl - r)^2 / 4.0
        cal | rl - r == 0.0 = 0.0
            | otherwise     = c * v
    print cal