import System(getArgs)
import List
import qualified Data.Set as Set

main = 
    do  
      args <- getArgs
      let n = read (args !! 0);  m = read (args !! 1)
      let ref = Set.fromAscList $ map (spread n) [0..(n*m-1)]
      putStr $ (show n)++" by "++(show m)++"\n"
      let oh_layouts = concatMap (\ohs -> generate ohs (n*m)) [((n*m)`div`4)..(n*m)]
      let best = head $ filter (valid' n ref) $ map (map (spread n)) oh_layouts
      putStr $ (show (length (best)))++" empty cells: \n"
      putStr $ chunk n $ show_garden n m best

spread n x = x + n*(x `div` n)

show_garden n m ohs = 
    [if (spread n x) `within` ohs then 'O' else 'X' | x <- [0..(n*m-1)]]

within val ohs = any (==val) ohs 

valid' n ref curr_garden = ref `Set.isSubsetOf` visible
    where 
        visible = Set.fromList $ 
                    concatMap (\x ->[x-2*n,x-1,x,x+1,x+2*n]) curr_garden

chunk n [] = ['\n']
chunk n xs = first ++ "\n" ++ chunk n rest
    where (first, rest) = splitAt n xs

generate sub total = gen total $ reverse $ take sub [0..]
  where
    gen total [] = []
    gen total xss@(x:xs) | x<total   = xss: gen total ((x+1):xs)
                         | otherwise = let r = gen (total-1) (incHead xs) 
                                           p = map (\ns -> (1+(head ns)):ns) r
                                       in gen total $ top p

top [] = []
top (x:xs) = x

incHead [] = []
incHead (x:xs) = (x+1):xs