import Data.Array
import Data.List (nub)

data Pos = Pos Int Int deriving (Eq,Ix,Ord,Show)

type Map = Array Pos Int

step :: Map -> Pos -> [Pos]
step m p@(Pos x y) = filter ((== 1) . subtract (m ! p) . (m !))
  . filter (`elem` indices m)
  $ steps
  where
    steps = [ Pos (x+1) y
            , Pos (x-1) y
            , Pos x (y+1)
            , Pos x (y-1)
            ]

width,height :: [[a]] -> Int
width = length . head
height = length

reachable :: Map -> Pos -> [Pos]
reachable m p | m ! p == 9 = [p]
              | otherwise  = concatMap (reachable m) $ step m p

score :: Map -> Pos -> Int
score m = length . nub . reachable m

trailheads :: Map -> [Pos]
trailheads = map fst . filter ((== 0) . snd) . assocs

parse :: [[Char]] -> Map
parse ls = listArray
           (Pos 0 0, Pos (width ls - 1) (height ls - 1))
           (map (read . pure) $ concat ls)

main :: IO ()
main = do
  m <- parse . lines <$> getContents
  print . sum . map (score m) . trailheads $ m