import Control.Monad
import Control.Applicative
import Data.List as List
import Data.Array as Array
import Data.Maybe as Maybe
import Debug.Trace

f a = do
  map ((\xs -> filter (== head xs) xs).(map (a !)).g) $ Array.indices a
  where
  r = Array.inRange $ Array.bounds a
  g (y, x) = filter r [(y + i, x + j) | (i, j) <- [(0,0),(0,1),(0,-1),(1,0),(-1,0)]]


main = do
  _ <- getLine
  s <- words <$> getContents
  --let s = ["#.#",".#."]
  let ly = length s
  let lx = (`div` ly).length.join $ s
  let a = Array.listArray ((0, 0), (ly - 1, lx - 1)) $ join s
  let b =  and.map (\xs -> (head xs == '#') && length xs /= 1) $ f a
  putStrLn $ if b then "Yes" else "No"
