let h, w, c = Scanf.scanf " %d %d" @@ fun a b -> a, b, ref 0
let _ = for i = 0 to h - 1 do for j = 0 to w - 1 do Scanf.scanf " %c" @@ fun a -> if a = '#' then incr c done done; print_endline @@ if !c = h + w - 1 then "Possible" else "Impossible"