type greeting = NYANPASS | OTHER | NA

let greeting_of_string =
  function | "nyanpass" -> NYANPASS | "-" -> NA | _ -> OTHER

let array_forall f arr = Array.to_list arr |> List.for_all f

let solve n arr =
  let rec solve' j result =
    if j >= n || (List.length result) > 1 then result
    else
      let isRentyon =
        array_forall (fun g -> g = NYANPASS || g = NA) arr.(j)
      in
      let nextResult = if isRentyon then j::result else result
      in
      solve' (j + 1) nextResult
  in
  let result = solve' 0 [] in
  match result with
  | j::[] -> j + 1
  | _ -> -1

let read_matrix n =
  let arr = Array.make_matrix n n NA
  in
  let rec read_matrix' i =
    if (i < n) then (
      let glst = read_line () |>
                 Str.split (Str.regexp_string " ") |>
                 List.map greeting_of_string
      in
      List.iteri (fun j g -> arr.(j).(i) <- g) glst;
      read_matrix' (i + 1)
    )
  in
  read_matrix' 0;
  arr

let () =
  let n = read_line () |> int_of_string in
  let arr = read_matrix n in
  solve n arr |> string_of_int |> print_endline