{-# OPTIONS_GHC -O2 #-}
{-# LANGUAGE BangPatterns          #-}
{-# LANGUAGE CPP                   #-}
{-# LANGUAGE LambdaCase            #-}
{-# LANGUAGE MagicHash             #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE MultiWayIf            #-}
{-# LANGUAGE OverloadedStrings     #-}
{-# LANGUAGE TupleSections         #-}
{-# LANGUAGE TypeFamilies          #-}
{-# LANGUAGE ViewPatterns          #-}

import           Control.Applicative
import           Control.Exception
import           Control.Monad
import           Control.Monad.Primitive
import           Control.Monad.ST
import           Control.Monad.State.Strict
import           Data.Bool
import qualified Data.ByteString             as B
import qualified Data.ByteString.Builder     as B
import qualified Data.ByteString.Char8       as C
import qualified Data.ByteString.Unsafe      as B
import           Data.Char
import qualified Data.Foldable               as F
import           Data.Function
import qualified Data.IntMap.Strict          as IM
import qualified Data.IntSet                 as IS
import qualified Data.List                   as L
import qualified Data.Map.Strict             as M
import           Data.Monoid
import           Data.Ord
import           Data.Primitive.MutVar
import qualified Data.Set                    as S
import           Data.Tuple
import qualified Data.Vector                 as V
import qualified Data.Vector.Generic         as G
import qualified Data.Vector.Generic.Mutable as GM
import qualified Data.Vector.Unboxed         as U
import qualified Data.Vector.Unboxed.Mutable as UM
import           Debug.Trace
import           Foreign                     hiding (void)
import           GHC.Exts
import qualified System.IO                   as IO
import           Unsafe.Coerce

main :: IO ()
main = do
    [h, w] <- map read.words <$> getLine :: IO [Int]
    mat <- U.unfoldrN (h*w) C.uncons . C.filter (\c -> c == '#' || c == '.') <$> C.getContents
    print $ solve h w mat

solve :: Int -> Int -> U.Vector Char -> Int
solve h w mat = U.maximum $ U.zipWith5 score mat left right up down
  where
    ix i j = i * w + j

    score '.' l r u d = l + r + u + d - 3
    score '#' _ _ _ _ = 0

    trans :: U.Vector Int -> U.Vector Int
    trans m = U.unsafeBackpermute m $ U.generate (h * w) $ \ij ->
        let (i, j) = quotRem ij w
        in j * h + i

    left :: U.Vector Int
    left = U.concatMap (\i ->
        U.postscanl' (\acc c -> if c == '#' then 0 else acc + 1) 0
        $ U.unsafeSlice (i * w) w mat
        )
        $ U.generate h id

    right :: U.Vector Int
    right = U.concatMap (\i ->
        U.postscanr' (\c acc -> if c == '#' then 0 else acc + 1) 0
        $ U.unsafeSlice (i * w) w mat
        )
        $ U.generate h id

    up :: U.Vector Int
    up = trans
        . U.concatMap (\j ->
            U.postscanl' (\acc c -> if c == '#' then 0 else acc + 1) 0
            $ U.map (U.unsafeIndex mat) $ U.iterateN h (+w) j
        )
        $ U.generate w id

    down :: U.Vector Int
    down = trans
        . U.concatMap ( \j ->
            U.postscanr' (\c acc -> if c == '#' then 0 else acc + 1) 0
            $ U.map (U.unsafeIndex mat) $ U.iterateN h (+w) j
            )
        $ U.generate w id


Measured memory_bytes: 183804