let h, w = Scanf.scanf "%d %d\n" (fun x y -> x, y)

let rec read_char acc = function
  | 0 -> acc
  | k -> read_char (Scanf.scanf " %c" (fun x -> if x = '#' then (acc + 1) else acc)) (k-1)

let () = print_string (if (read_char 0 (h*w)) = h+w-1 then "Possible" else "Impossible")