import qualified Data.Text as T
import qualified Data.Text.IO as T
import qualified Data.Text.Read as T

main :: IO ()
main = do
  (n : m : _) <- map unsafeTextToInt . T.words <$> T.getLine :: IO [Int]
  print $ ((n * (pred n)) `div` 2) + ((m * (pred m)) `div` 2)

unsafeTextToInt :: T.Text -> Int
unsafeTextToInt s = case T.signed T.decimal s of
  Right (n, _) -> n
