Problem:
Score: 400 points

Problem statement

We have an H \times W grid whose squares are painted black or white. The square at the i-th row from the top and the j-th column from the left is denoted as (i, j).

Snuke would like to play the following game on this grid. At the beginning of the game, there is a character called Kenus at square (1, 1). The player repeatedly moves Kenus up, down, left or right by one square. The game is completed when Kenus reaches square (H, W) passing only white squares.

Before Snuke starts the game, he can change the color of some of the white squares to black. However, he cannot change the color of square (1, 1) and (H, W). Also, changes of color must all be carried out before the beginning of the game.

When the game is completed, Snuke's score will be the number of times he changed the color of a square before the beginning of the game. Find the maximum possible score that Snuke can achieve, or print -1 if the game cannot be completed, that is, Kenus can never reach square (H, W) regardless of how Snuke changes the color of the squares.

The color of the squares are given to you as characters s_{i, j}. If square (i, j) is initially painted by white, s_{i, j} is .; if square (i, j) is initially painted by black, s_{i, j} is #.

Constraints

H is an integer between 2 and 50 (inclusive).

W is an integer between 2 and 50 (inclusive).

s_{i, j} is . or # (1 \leq i \leq H, 1 \leq j \leq W).

s_{1, 1} and s_{H, W} are ..

Input

Input is given from Standard Input in the following format:

H W
s_{1, 1}s_{1, 2}s_{1, 3} ... s_{1, W}
s_{2, 1}s_{2, 2}s_{2, 3} ... s_{2, W}
: :
s_{H, 1}s_{H, 2}s_{H, 3} ... s_{H, W}

Output

Print the maximum possible score that Snuke can achieve, or print -1 if the game cannot be completed.

Sample Input 1

3 3
..#
#..
...

Sample Output 1

2

The score 2 can be achieved by changing the color of squares as follows:

Sample Input 2

10 37
.....................................
...#...####...####..###...###...###..
..#.#..#...#.##....#...#.#...#.#...#.
..#.#..#...#.#.....#...#.#...#.#...#.
.#...#.#..##.#.....#...#.#.###.#.###.
.#####.####..#.....#...#..##....##...
.#...#.#...#.#.....#...#.#...#.#...#.
.#...#.#...#.##....#...#.#...#.#...#.
.#...#.####...####..###...###...###..
.....................................

Sample Output 2

209

Solution in Haskell (GHC 7.10.3) (judge verdict: Accepted)

import Control.Monad
import Control.Applicative
import Data.List
import qualified Data.Map as Map
import Data.Array
import qualified Data.ByteString.Char8 as BC
import Data.Maybe
import qualified Data.Set as Set
import qualified Data.Sequence as Sq
import Data.Sequence (ViewL(..),ViewR(..),(><),(<|),(|>),Seq)

bsreadInt :: BC.ByteString -> Int
bsreadInt = fst . fromJust . BC.readInt
strToInt s = (read :: String -> Int) s

main = do

    [h,w]<- map bsreadInt . BC.words <$> BC.getLine
    ss <- replicateM h BC.getLine
    let s = BC.filter(/='\r') $ BC.concat ss
    let grid = array ((1,1),(h,w)) [((i,j), BC.index s ((i-1) * w + (j-1))) | i<-[1..h],j<-[1..w]]
    
    let chk = Set.singleton (1,1)
    let q0 = Sq.fromList [(1,1)]
    let q =  q0 <| Sq.empty
    let white = BC.length $ BC.filter(=='.') s
   
    if (Sq.length (move q h w grid chk)) == 0 then print (-1)
                                          else print $ white -  Sq.length (move q h w grid chk) 
    
adjblock :: (Int,Int) -> Int -> Int -> [(Int,Int)]
adjblock (m,n) h w
   | m==1 && n==1 = [(2,1),(1,2)]
   | m==h && n==w = []
   | m==h && n==1 = [(m-1,n),(m,n+1)]
   | m==1 && n==w = [(m+1,n),(m,n-1)]
   | m==1 = [(m+1,n),(m,n-1),(m,n+1)]
   | n==1 = [(m-1,n),(m+1,n),(m,n+1)]
   | m==h = [(m-1,n),(m,n-1),(m,n+1)]
   | n==w = [(m-1,n),(m+1,n),(m,n-1)]
   | otherwise = [(m-1,n),(m+1,n),(m,n-1),(m,n+1)]

sqleft :: Seq a -> a
sqleft q = sqleft_(Sq.viewl q)
sqleft_ :: ViewL a -> a
sqleft_ (x :< xs) = x
sqright :: Seq a -> a
sqright q = sqright_(Sq.viewr q)
sqright_ :: ViewR a -> a
sqright_ (xs :> x) = x

--movestep :: [(Int,Int)] -> Int -> Int -> (array (Int,Int)) -> [[(Int,Int)]]
movestep qa h w grid chk = [(i,j) | (i,j) <- (adjblock (sqright qa) h w ) , (grid ! (i,j)) == '.' , Set.member (i,j) chk == False]

--move :: (Seq [[(Int,Int)]]) -> Int -> Int -> (Array (Int,Int)) -> [(Int,Int)]
move q h w grid chk = if Sq.length q == 0
                      then Sq.empty
                      else if sqright (sqleft q) == (h,w)
                           then sqleft q
                           else move q2 h w grid chk2
                                where qa = sqleft q
                                      q2 = (Sq.drop 1 q) >< (Sq.fromList add)
                                      add = [qa |> x |x <- (movestep qa h w grid chk)]
                                      chk2 = Set.union chk (Set.fromList (movestep qa h w grid chk))