heron a b c = sqrt ((a + b + c)*(-a + b + c)*(a - b + c)*(a + b - c)) / 4

solve a b c = 2 * s / (a + b + c)
  where s = heron a b c

main :: IO ()
main = do
  [a, b, c] <- map read . words <$> getLine :: IO [Double]
  let ans = solve a b c
  print ans