doit :: Int -> Int -> Int -> Int
doit size right down
  | right == size && down == size = 1
  | right == size = doit size right (down+1)
  | down == size = doit size (right+1) down
  | otherwise = sum [ doit size (right+1) down
        , doit size right (down+1) ]

doit2 :: Int -> Int -> Int -> Int
doit2 size right down
  | right == size = (size+1)
  | down == right = doit2 size (right+1) down
  | otherwise =
      sum [ doit2 size (right+1) down
          , doit2 size right (down+1)
          ]

main = do
  print $ "Calculate 20x20"
  print $ doit2 20 0 0