let [|H; W|] = stdin.ReadLine().Split() |> Array.map int

let count = 
    List.sum [ for _ in 1..H -> 
                 stdin.ReadLine().ToCharArray()
                 |> Array.filter (fun x -> x = '#')
                 |> Array.length]

if count = H + W - 1 then "Possible" else "Impossible"
|> stdout.WriteLine
